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Old 08-16-2011, 07:34 PM   #1
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1995 SW2
Default SW2 Idle Woes

Hi All...

I've got a 1995 SW2 with a really stubborn idle problem. We'll chalk this up to a learning experience.

First, the car drives just fine. It has power, it gets up to highway speed and, as long as it is motion, doesn't seem to have any driveability problems. But, when you come to a stop, the idle will be very rough. The engine doesn't miss but it lugs and a normal idle speed of ~800rpm can drop down to about 500 or so and back up. The engine rarely stalls in this condition but it can. The fun part is that the car will idle just fine, like nothing is wrong, if it's shifted into neutral or park. The engine sounds completely normal when in these gears. When driving, the engine sounds completely normal. There's only a problem when stopped and the RPMs go to idle in a drive gear (reverse included, though I have not tested that too closely). The car is getting significantly worse mileage since this problem developed.

As part of trying to figure out what's going on, I noticed the alternator was bad and replaced it and the belt. The car has also recently had a coolant flush. I installed a new ETCS last year. The engine needs a new top mount, which is making the idle vibration problem worse-- but it can't be the whole problem because of the lugging and RPM changes.

At first I thought it might be the IAC. Stupidly, I just up and replaced the thing. Likewise the TPS has been replaced. I don't really like throwing parts at problems, but with a 1995 car, if I replace it now it won't break on me later (hopefully). I checked the ignition coils as well; the resistances are in spec for both coils for both primary and secondary. I installed new plugs and wires last year. I just ran the car with a soda can between the engine and the EGR, and that didn't help either. I cleaned the EGR recently, and again yesterday. I checked the intake manifold for leaks with both carb cleaner and running some MAPP gas around the mating surface with the head... it seems fine.

The major culprit here could be a leak in the canister purge value, but I don't have a single code in the PCM (and this is OBD-I so there might not even *be* a code for this-- I don't know of one anyway). I checked it awhile back, and the vac hose from the valve to the canister was pretty cracked where it mates with the valve... I replaced that hose, and the problem persisted. I've also put the car up and tested the vacuum directly on the valve. This is the weird part... the intake port of the canister purge valve holds vacuum. I checked this at the top of the line at the throttle body and the entire line holds vacuum (incidentally the fuel regulator line holds vacuum too). I also checked it directly on the purge valve... it holds vacuum on the intake port. However, on the port that connects to the canister, it does NOT hold vacuum... it bleeds away in seconds.

So I'm almost at my wits' end... is this a bad purge valve? Or is something else going on? I keep on eliminating what the problem isn't, but not what it is! This is seriously acting like a vacuum leak, but with that one exception on the canister port of the purge valve, the system seems to hold vacuum.

Please help!
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Old 08-17-2011, 02:10 PM   #2
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1995 SW2
Attention Re: SW2 Idle Woes

Addendum: I checked the fuel pressure as well today: it's 36psi and the hold pressure at 5 minutes was 42psi. So whatever this problem is, it's not for lack of fuel. I just dumped a big bottle of Techron into the tank and hope for the best-- it might be a messy injector or something too.
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Old 08-17-2011, 07:06 PM   #3
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2000 SL1
Default Re: SW2 Idle Woes

My 2000 is happy above 1000rpm. Below that, it runs roughly. Only does it sometimes, though. Sometimes it idles like new, other times it runs like it's missing on 2/4 cylinders.
Random misfire code and pretty even spark plug wear doesn't yield any results. Does it in any gear (automatic) and in any weather condition, at any engine temperature. Coils, wires, plugs and ICM have been replaced.
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Old 08-17-2011, 08:49 PM   #4
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Default Re: SW2 Idle Woes

Hello Fingol-
hopefully you get more/better responses.
I would try checking the fuel pressure regulator's response to varying vacuum.
The regulator diaphragm may be leaky.......
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Old 08-18-2011, 10:56 AM   #5
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1995 SW2
Attention Re: SW2 Idle Woes

Yeah, pressure regulator's on the list of things-to-do. Last night I checked the canister purge valve again on a whim and it didn't hold vacuum on the intake side. It could be an intermittent fault in the thing... I'm going to just check it on the valve itself (and hopefully find an angle where I can see the bloody thing). If it fails, I'll just replace the valve. It needs to hold vacuum on the intake side when closed. The fuel regulator line holds vacuum, but when I check the purge valve again I'll do a check right on the regulator and not just on the top of the vacuum line at the throttle body.

I hope I get more responses too... but regardless I'll keep posting to this thread. Purge valves on these engines get a lot of coverage here, but this appears to be a multilayered problem with the motor mounts as well. This might help someone else down the road.

Incidentally, I put the car up again last night to check the valve this morning. I spun the driver's side front tire and the engine moved.... time for new mounts!
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egr valve, evap purge valve, rough idle under load

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