Dirty throttle body = stalling, but why?

[d0ugparker]

In a different post's answer (I hope I'm not hijacking a thread, here)

Originally Posted by OldNuc

If the car was running fine and now it starts and dies the first thing to do is remove and properly clean the throttle body per the richpin video. A dirty TB will cause the engine to stall.

it states a dirty TB till cause engine stalls... but why?I'm thinking it has to do with air flow, but I can't figure it out.

[toggenburg]

When soot and grime build up inside the throttle body and it's pintle shaft, it causes improper air flow. The TB is designed to remain partially open when the gas pedal is released to keep the engine running. Keep it clean inside.

[fdryer]

Unless you're willing to set aside time to learn how EFI systems replaced old school carburetors and distributors with all electronic EFI systems, a dirty throttle body only addresses physical issues that in and of itself may not explain why engines stall. There's more to this than just correlating engine stalling from a dirty throttle...... much more.

To begin with a throttle body used in the S-series engines (1.9L), look up its parts then review what those parts do. You may get sucked into the world of EFI systems. It helps to learn how 4-stroke engines run to have an overall perspective as you progress into understanding how engines run. Just remember it's not rocket science. Your father or grandfather having basic skills may have been one of hundreds of thousands of ground crew maintaining WWII aircraft, trucks, tanks with nothing more than a high school education yet helped win WWII. Education not taught anymore due to computers. Skills taught decades ago still apply today since car engines haven't changed and still operate on the same 4-stroke principal as engines did in WWII. The major change was electronics when EFI systems became the standard for more reliability and less maintenance needed. Electronics skills are needed to understand sensors and solenoids help engines along with how engine computers operate EFI system.

[alordofchaos]

Originally Posted by d0ugparker

In a different post's answer (I hope I'm not hijacking a thread, here)

No, you're good.

You'd only be hijacking if you posted your question on the other thread, taking it off course from what the original poster (OP) was talking about. Usually occurs like this:

OP: Hey, I have issue A. Can anyone help?

Forum members: discusses issue A but has not concluded with resolution.

Hijacker: Hey, I have a similar issue

Forum members: start talking about Hijackers issue

Forum members: get confused between OP's issue and hijacker's issue or facts (hey, I thought your car was an '02. No, that was the other guy)

[d0ugparker]

"It's complicated." I get it.

My car would randomly stall, when accelerating, usually from a dead stop. Sometimes, it seemed to work as if it was functioning fine, overall, although its acceleration seemed lackluster (symptom!).

During the times when it was working in "I'm fine" mode, waiting at a light, there'd be a brief engine shudder (symptom), and it would shut off "I'm fine" mode and would now seem to be in "not fine" mode. I could pretty much count on it stalling as I tried accelerating away at the next green light (symptom)--if it didn't stall while I was sitting there standing still. Once in a while the stall would happen when I wasn't moving.

In "not fine" mode, at a green light, I'd start moving a bit, I'd stall, people would start honking their horns behind me (like that's going to help anything, people? Right? (-; ), I'd anxiously restart, stall, restart, stall, and eventually get moving again (symptom), and once I was up and moving, I was generally okay (symptom). Speed was my friend. Speed = no stalling. That was my (armchair technician) proof it wasn't a fuel filter issue.

Over the last few days, I read through the forum and found out about the carbon buildup. I removed the throttle body and cleaned it out, removing the TPS and the AIC, and dusting off the AIC. (what're the sleeve and spring's purposes in the AIC's tip?)

After its cleaning last night (160,000 miles), I did a quick shake down ride. No stalls--yet--and, as an added surprise, the acceleration was much stronger than it had been. (not a symptom, but a good indicator)

Airflow. A butterfly valve designed to be slightly open when moving and when stopped to keep the engine from stalling. A BV that was engineered to have zero interferences affecting its airflow rate. A BV whose programming goes wanky when enough carbon deposits get in the way to throw its mathematical model into a tailspin. It's just doing what it was programmed to do with zero carbon buildup... only now it's got carbon buildup, but it can't sense that. "It's complicated."

I'll monitor things as I go. I use the car for deliveries, so I've got plenty of paces to put it through.

Please click the upvote button.

TY

[alordofchaos]

Originally Posted by d0ugparker

Over the last few days, I read through the forum and found out about the carbon buildup. I removed the throttle body and cleaned it out, removing the TPS and the AIC, and dusting off the AIC. (what're the sleeve and spring's purposes in the AIC's tip?)

Idle Air Control (IAC) valve seals or opens a side passage in the throttle body, to let more or less air in as needed for varying operating conditions - differing temperatures on cold starts vs warm starts, when idling with AC on (engine will automatically idle a little higher), closed throttle deceleration, etc.

[hholbein]

Originally Posted by alordofchaos

Idle Air Control (IAC) valve seals or opens a side passage in the throttle body, to let more or less air in as needed for varying operating conditions - differing temperatures on cold starts vs warm starts, when idling with AC on (engine will automatically idle a little higher), closed throttle deceleration, etc.

+1

When you're cleaning your Throttle Body, it pays to be careful about spraying carb cleaner into the IAC passages. The electronics of the controller can get messed up.

[d0ugparker]

Originally Posted by hholbein

*
When you're cleaning your Throttle Body, it pays to be careful about spraying carb cleaner into the IAC passages. The electronics of the controller can get messed up.

Yes, TY.

The IAC was removed, its passages were cleaned, with a dry cloth, or a cloth that had been sprayed, itself, far away from the IAC, and the IAC was reinstalled.

Any spray product with "California health warnings" on it, all the benzenes, toluenes, and other -enes available, well, they just seem a tad too exotic, harsh, harmful, damaging, and toxic to be spraying at innocent IACs.

[fdryer]

Originally Posted by d0ugparker

"It's complicated." I get it. .....My car would randomly stall, when accelerating, usually from a dead stop. Sometimes, it seemed to work as if it was functioning fine, overall, although its acceleration seemed lackluster (symptom!). .....After its cleaning last night (160,000 miles), I did a quick shake down ride. No stalls--yet-- .....

Airflow. A butterfly valve designed to be slightly open when moving and when stopped to keep the engine from stalling. A BV that was engineered to have zero interferences affecting its airflow rate. A BV whose programming goes wanky when enough carbon deposits get in the way to throw its mathematical model into a tailspin. It's just doing what it was programmed to do with zero carbon buildup... only now it's got carbon buildup, but it can't sense that. "It's complicated."......

You're missing some things not discussed at length with EFI systems.

The idle air control valve is the PCMs way of adjusting all idle speeds from subzero cold to desert heat along with ac use and various electrical loads. The fixed throttle plate opening was preset at factory assembly. The iacv, as commanded by the pcm from various sensors, adjusts the iacv for final idle rpm. This is only one part of a complicated EFI system.

1-What's your idle rpm on cold engine startup. What's warm engine idle rpm?

2-Did you replace the infamous coolant sensor, next to the egr valve? Original round nosed plastic sensors fail by cracking and sending erroneous temperature signals as if the engine is in subfreezing cold. This is interpreted by the pcm to flood the engine with excess fuel on startup and continue in rich fuel mode, never sending correct temperature signals to the pcm. A computer is only as intelligent as its weakest sensor. The cure has always been to remove the sensor, verify its the round nosed one and replace it with a flat nosed brass one. Instant starting, coolant signals and temperature gauge are changing as the engine warms up, idle adjusts automatically as engine operating temperature are reached, and many other things fall into place. Stalling goes away.

The temperature gauge hovering over the 1/4 mark is a tell tale indication. And overheating is another hint. Damage from a faulty coolant sensor also melts the rubber seal used in the thermostat, rendering the cooling system running cooler than normal. Overheating occurs despite this because the cooling fan never turns on from a faulty coolant sensor.

It's complicated.

[d0ugparker]

Yeah, complicated. Checking the data points tomorrow morning on a cold block.

I bought a new, flat head brass Engine Coolant Temperature Sensor, because it's my next suspect.

...now, where's that FAQ...

Thanks for your support. I'm a great, fantastic dog trainer, but when it comes to auto repair, unless I've got a good support team behind me, I'm not that great of a wrencher.

[d0ugparker]

Originally Posted by d0ugparker

I bought a new, flat head brass Engine Coolant Temperature Sensor, because it's my next suspect.

I replaced the ECTS, but dang it, the old one was flat-tipped brass. Because it wasn't an older, plastic-tipped unit, I wasn't expecting promising results. The results weren't good—the vehicle still managed to stall one time when hot. Only once though, not six or eight, like in the old days: the day before yesterday.

The old "sitting at the stoplight" pattern was a twelve second cycle of approximately

1. six seconds of rough idling and almost stalling (old pattern), followed by
2. six seconds of smooth, reasonable idling (old pattern).

I didn't test its AC on versus AC off state. This is old data, now. I'm only reporting it for completeness.

The new, ECTS replacement resulted in, subjectively, significantly improved cold acceleration, but hot acceleration seemed to fade away entirely. It makes me wonder if TPS is being ignored when hot... but then there might be other causes I don't know about yet.

RPMs seem normal, AC on or off, during idle times, although I can't quote them, didn't write them down yet, and seem to be reasonable. If I remember correctly,

1. 800 RPM idle AC on
2. 1,100 RPM idle AC off

Starting is not instant. It usually takes a second or third crank to take. Sometimes it will start on the first crank, but rarely, and the catching of the idling is sloppy and not solid nor defined. It like it kind of wants to start—it does't start with definition or strength. It's weak, sluggish starting.

It did stall once, last night, in a 90 minute period. Extremely careful, slow acceleration keeps the car moving forward without stalling. I've tried tapping on the accelerator during these extremely slow acceleration periods, and the throttle position oftentimes (yet rarely, if ever) seems to be detected. There's no surging feeling, no increase in acceleration synchronized with every accelerator pedal push. The pedal's being pushed, but when the engine gets hot, there seems to be a disconnect.

Your quote about "the engine is only as good as its weakest sensor" is so true: I'm still not sure of what sensor it is that's crying for replacement, yet.

[billr]

Quit guessing, use live-data to see what those sensors are reading.

Since things seem a bit better after swapping the ECT sensor for a new one, I'm suspicious of the wiring/connector to the ECT sensor... but that's just a guess!

[focusofheart]

Let me jump in and put both feet into my mouth (salt, salt, salt) and suggest you clean the EGR, if that wasn't already done. It is a simple process that even this great grandma has done with good results.

Do a search on this forum for tips and grab your 10mm socket and some coffee.

https://www.youtube.com/watch?v=811LzycZpX8

hint: after you take off the EGR, start up the car for a few seconds to blow some carbon out. OldNuc gets credit for that tip.

http://www.saturnfans.com/forums/sho...d.php?t=137357

[fdryer]

Originally Posted by d0ugparker

1. 800 RPM idle AC on
2. 1,100 RPM idle AC off

Starting is not instant. It usually takes a second or third crank to take. Sometimes it will start on the first crank, but rarely, and the catching of the idling is sloppy and not solid nor defined. It like it kind of wants to start—it does't start with definition or strength. It's weak, sluggish starting...........

Something's wrong. Ac compressors always loads an engine down. With EFI systems, programming in the pcm automatically bumps idle rpm 100-200 rpm up (depending on engine size) to maintain the same idle with ac on. Ac on with idle@800 rpm is fine. Ac off with 1100 rpm is wrong. Warm idle should be a few hundred rpm lower not 1100. Examine the chart below. Without a load (other than alternator and power steering pump always running), idle should be around 650-850 rpm.

There may be an air leak allowing more air into the engine than desired and throwing off the EFI system (stalling, poor startup, hesitation). You'll need to check for vacuum leaks by using a water spray from a bottle (Windex bottle, other hand sprayers). With engine idling, spray around the throttle body to intake manifold, testing for a gasket leak. Spray around the intake manifold to engine block, testing for the same gasket leak. Water ingested into a damaged gasket or loose nuts or bolts will reduce rpm immediately as water is drawn into the vacuum leak, momentarily blocking off air flow resulting in a drop in rpm. If the throttle body gasket or intake manifold gasket isn't damaged, rpm will remain high.

[Signmaster]

Good suggestions on both of the above. If you are getting air through either gasket leaks or EGR leaks, it's not properly compensated for. For that reason the throttle position doesn't jive with the actual air flow, which impacts fuel, timing, etc.


I would also test the IAC. For basic tests, observe from a cold start if the car starts at higher RPM idle then gradually tapers idle RPM down as the coolant warms up. The 1,100 stated is high, and I don't think any factory spec shows that as acceptable. Most cars idle in the 700-900 range regardless of AC use.

At any rate, once the car is up to full temp (a quick trip might help once you determine start up characteristics) you can remove the air intake hose to the TB. If you cover the small hole that is outside of the throttle body butterfly, the idle should go all the way down to 500-600 RPM. If it isn't that probably indicates either a vacuum or EGR leak as mentioned in posts above, or possibly that someone has screwed around with the butterfly plate adjustment screw.

[d0ugparker]

(I wanted to Multi-Quote to reply to three posts at once, but nothing happened when clicking each multi-quote icon below their separate posts. Maybe it's a Chrome anomaly.)

Originally Posted by focusofheart

...clean the EGR.

Originally Posted by fdryer

Something's wrong.

Originally Posted by Signmaster

I would also test the IAC.

Thanks all. I think my 1,100 data point is bad. I need to go back and pay closer attention to the RPMs when hot. On the EGR, IAC, and recording new data points, my work is cut out for me for a bit. Thank you.

Yesterday? Zero bad performance—I mean zero, in five hours of driving. Go figure. What I don't like about it is now I may be chasing an intermittent ghost in the machine.

Does the ECM "remember" past, bad data, slowly purge the old, bad, data, and refresh the old data with new sensor data, running the engine better and smoother as time goes by? I really don't know how else to make the car's performance fit its evidence. Too, let's see how today's performance fits into the fray.

[d0ugparker]

I've now had two days of stall-free operation. It still takes an average of 1.5 cranks per start to get 'er started. I read somewhere that it's supposed to be instant starts--1.0 cranks per start. Is that a new symptom?

Originally Posted by Signmaster

Most cars idle in the 700-900 range regardless of AC use.

This is consistent with the car's new pattern.

If the ECTS was the only thing changed, and it's now running reliably, the old ECTS was bad, or the connector or wiring was flaky. The old connector was dry, with no apparent oxidation.

Next, as billr suggested, "Stop guessing." So, how do I confirm the old ECTS is bad? What's the resistance reading on a functioning unit, and does it need to be verified in hot and cold conditions to confirm it's broken? If I can confirm a busted ECTS, that would ease my mind tremendously.

(I just remembered that before the ECTS change, when I was running with no AC, when it would start to stall, turning on the AC would goose the RMP enough to seem to keep it from stalling. I don't know that that matters now, though.)

[billr]

You could take the ECT sensor out and test resistance in both ice-water and boiling water and post results; we would confirm they are correct. Or do a search here for "ECT", that chart has been posted many times.

However, that won't confirm what the PCM is reading at the other end of the circuit. You need live-data for that.

[alordofchaos]

Originally Posted by billr

Quit guessing, use live-data to see what those sensors are reading.

There are a few threads describing Bluetooth Elm327 clones and inexpensive phone apps that you can get for reading live data. Total should run $10~$40 depending on what you buy.

Live data is valuable for troubleshooting.

Since things seem a bit better after swapping the ECT sensor for a new one, I'm suspicious of the wiring/connector to the ECT sensor... but that's just a guess!

Just an anecdote, but the first time I replaced my (clearly cracked, round resin-tipped - car stalled constantly, was nearly undriveable) ECTS, I saw zero improvement. I tried cleaning out the ECTS connector, same.

Had to replace the ECTS connector (soldered in) and had zero problems after that.

[d0ugparker]

Yesterday saw a handful of stalls, dang it.

Idling with AC off is about 750 rpm, and a tad on the rough side, by my estimate. When the AC is kicked on, the smoothness returns, but the rpm increases a touch as well, so the smoothness comes partly from the slight speed increase.

I'll investigate the connector at some point. I have to google the live data connection. I'm not too happy going that route at the moment.