Throttle Hesitation After Cold Start

[MetalMatty]

I did some searching and nothing really seemed to describe the issue I'm having.

I have a 1998 SL2 with 150k. Five speed.

It runs fairly well, I keep up on maintenance. In the past 6 months I've done plugs, (wires looked like they've been recently replaced and are in the correct order), took off throttle body and EGR valve for cleaning.

The issue I have only occurs after a cold start. Not IN THE COLD, just a start where the engine is not at operating temp. When I start the car I always let the fuel pump prime first.

After the car has started and idle settles to its 1100-1300:

If I give e throttle a light jab (as if pulling away from a stop light) the car will almost stall, and occasionally does. If I just jab once, the throttle drops and the car shakes then revs rise up and it catches itself. If I jab multiple times it will stay down around 3-500 rpm very near stalling. Usually after I jab, let it save itself, and jab again 2-4 times it will be fine and I can jab the throttle and it revs like it should.

I think in my days off im going to pull the coil packs and see if anything is corroded and spray some carb cleaner around #1 intake port but wanted to post to see if you guys had any ideas in the mean time.

Video of the problem: http://youtu.be/tL_d-NtwFA8

- Matt

[OldNuc]

Does the idle come down to the ~800RPM range when warm? If it does you problem is it is running way rich when cold.

ECTS
IAT
OEM TPS
Minute exhaust leak

Any or several will cause this problem.

If everything above is OK then check exhaust between engine head and CAT inlet.

Exhaust leak check.
--Locate a low pressure high volume air source, reversible vacuum cleaner, large fan, leaf blower or what ever you can find.
--Loosely couple to cold exhaust at the tail pipe, or direct fan at tail pipe.
--Spray every inch of the exhaust between the head and CAT inlet with a mixture of 2 or 3 drops of dish soap and water in a spray bottle.
--Pay close attention to the lower flange, lower support clamp, and flex connector.
--The flex connector is under the protective braid so it requires quite a bit of solution to show any leaks.

[MetalMatty]

Originally Posted by OldNuc

Does the idle come down to the ~800RPM range when warm? If it does you problem is it is running way rich when cold.

ECTS
IAT
OEM TPS
Minute exhaust leak

Any or several will cause this problem.

If everything above is OK then check exhaust between engine head and CAT inlet.

Exhaust leak check.
--Locate a low pressure high volume air source, reversible vacuum cleaner, large fan, leaf blower or what ever you can find.
--Loosely couple to cold exhaust at the tail pipe, or direct fan at tail pipe.
--Spray every inch of the exhaust between the head and CAT inlet with a mixture of 2 or 3 drops of dish soap and water in a spray bottle.
--Pay close attention to the lower flange, lower support clamp, and flex connector.
--The flex connector is under the protective braid so it requires quite a bit of solution to show any leaks.

Idle does rest around 800 when warm.
ECTS is new.
I am half tempted to think its exhaust problems. There are very small pin holes around the second cat. Unfortunately I can't afford a new exhaust. Especially a cat.
Which is why I wanted to start elsewhere. Is there a way to test and/or clean IAT and TPS short of replacing new?

[OldNuc]

Problem is those holes. Run the pressure test of exhaust and find all of them. Holes in pipe can be fixed, hole in cat not so much. Once you find and get some pix of th holes I can tell you how to DIY fix them. Be sure to check all of the manifold gaskets, both at the head and between manifold and pipe.

[MetalMatty]

Originally Posted by OldNuc

Problem is those holes. Run the pressure test of exhaust and find all of them. Holes in pipe can be fixed, hole in cat not so much. Once you find and get some pix of th holes I can tell you how to DIY fix them. Be sure to check all of the manifold gaskets, both at the head and between manifold and pipe.

I'll try and get some pics this week. They're right where the cat meets the pipe. Would some exhaust putty work?

[OldNuc]

I am guessing a decent exhaust shop could weld it up. and It is possible you may be able to patch it yourself. Plain exhaust putty alone will not stay in place.

Run that leak check to make sure there are no more holes.

[MetalMatty]

I actually put in a new IACV (Idle Air Control Valve) after I remembered slightly similar issues on my 2000 SL2.

Fixed the problem after a few cold - hot - cold cycles.

No more hesitation like before.

Though I am still going after the exhaust leaks.

[SL19302]

Those pin holes in that front exhaust pipe are whats causing the rich condition, If you have a scan tool that displays live data im sure the rich condition would be reflected in the long term fuel trims.

[MetalMatty]

Originally Posted by SL19302

Those pin holes in that front exhaust pipe are whats causing the rich condition, If you have a scan tool that displays live data im sure the rich condition would be reflected in the long term fuel trims.

Well like I said the terrible hesitation was my main concern and that is gone now.

It is still running rich while it warms up. My nose lets me know haha.

I'm currently deciding on what I'm doing exhaust wise. I'm gonna have my local Monro smoke test it so I know what I'm dealing with. If I can get away with a new cat and obx catback that's my plan.

[OldNuc]

By design they run rich when cold but they do not run rich after running for 3-4 minutes regardless of coolant temps. Once warmed up though a defective ECTS can force you into a rich-high idle condition but that will not set a 172 code.