For weeks, I have bveen trying to troubleshoot my rough idle problem. It doesn't do it when the engine is cold, only when it is hot. Sometimes the idle is so bad that it almost feels like it will stall (but never has).

So far I have done the following:

-Replaced Fuel pressure regulator
-New plugs
-New cap & rotor
-Re-soldered the fuel pump relay (just to rule that out)
-Cleaned the TB
-Cleaned the flame trap
-Looked/listened for vaccum leaks...none found
-Cleaned the air control valve

A month ago, the car was running so poorly due to an unplugged Fuel Injection connector. I connected it back and it ran fine, but now the rough idle was the problem.

Car runs perfectly fine when I give it a little gas...over 1000rpm, which says the trouble is something related to idle mechanism (duh!), but which one?

I am somewhat skeptical about the ACV....could this be operating fine during cold and poorly during warm, or do I have vaccum leak?

Any suggestion is appreciated...

TIA!
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

I have succesfully solved rought idle with the following (apart from the obvious vacuum check etc)

-Fuel filter
-Pre fuel pump electrical connecton (check for current at tank connection)
-Alternator regulator (irregular voltage)
-Idle switch repair/adjust
-Clean CIS valve
-Fuses (replace all with new (correct amps) few $$, great result)

Here's a shot in the dark, literally. How old are your plug wires. Park your car at night somewhere dark, with no outside lights, start it and look for arcs from your wires, I've had some pretty crappy idle from this condition. No more Pep Boys wires for me!!!
Good Luck.
Chuck///
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Chuck Jaxel, Pine Hill NJ, Near Philly...

Sirmebes, I've got the exact same problem in my car, so I totally understand how frustrating it can be!!!!!

I have a K-jet, and like you, my rough idle only occurs when warm. I too have blasted the IAC with carb cleaner.

This morning I sprayed out the throttle body with cleaner, and I the process I discovered 3 cracks in my vacuum hoses!!! I had enough slack in the hoses so that I could cut off the bad sections and still reach fine. I thought my problem would be solved, but now it's worse!

I think the vacuum leaks were making my idle a little bit higher, which prevented the car from stalling. Now it stalls when it used to just stumble. I think it may be the IAC, but I not ready to shell out $100 for a new one from IDP.

New development: when I turn the AC on, the car idles perfectly. No stalls, no stumbles. Sirmebes, see if yours works OK when the AC is on.

Intake air leaks are a definite possibility for rough running, but the engine may simply be running rough and tending to stall because the idle is swinging too low and getting stuck there. You can usually verify this by solidly tapping on the idle air control valve during a low, rough idle and see if the revs rise and the engine smooths out a bit. Although you've cleaned the IAC air passageway, the motor segment may be worn or dirty. The motor commutator will often get a wear area where it's used the most, i.e. warm idle. That's why it may work okay at the higher cold idle on a less worn area. With the older style 3-wire IAC and a little effort you could open the IAC motor and attempt to clean the commutator segment. However your LH 2.4 system will have the newer 2-wire, spring return style IAC motor that doesn't seem repairable. Before you give up on it, you could try working some penetrating oil around the motor shaft bushing in the air passageway. Work the valve back and forth by quickly twisting it in your hand or by rotating the valve with something non-scratching.
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Dave -not to be confused with a real expert, just goofing around at this

I cleaned it using carb cleaner....sprayed a whole lot down down and a lot of crap came out...maybe by cleaning it I made it worse :-)

I will try some penetrating oil.

Thanks
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

Sirmebes,

When was the last time you replaced the fuel filter? I had some rough idle issues (still do) which were helped by a new filter. My car is also a 1990.

This is a BIG shot in the dark but if your car has a manual tranny, have you had your clutch replaced anytime recently? My clutch was replaced (non-Volvo guy) when I bought the car a year ago. Have been trying to diagnose the idle problem practically from Day 1, found some things that helped, mostly vacuum leaks but to this day it still isn't solved. I just recently realized that the flywheel needs to be positioned the same way it came out...from looking at how far off my timing is (like 45-50 degrees) it seems plausible to me that my flywheel was installed incorrectly (especially since it was a non-Volvo guy). My car runs decent off idle, and gas mileage hasn't been affected much (within City/Highway spec). Considering my timing is so far off, it's amazing the car even runs.

Check your filter first. ;) Good luck.
Zuda

well, I could replace it and see wher it take me.

Thanks again,
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

Pull the intake snorkel off - all the way off - and look at the underside. I bet you'll find at least pinhole leaks, if not tears. Duct tape fixes it for today until you can get a replacement. And if that's not it, check all the little vacuum lines under the hood.

Sirmebes,
You situation really sounds, to me, like a vaccum leak. Did you use the spray bottle method around the intake? Are you absolutely sure you checked the intake hose? Are all the rubber hoses and their associated connections sound? All of the work and parts you replaced certainly rules out an entire list of problems... which leads me to believe that you may have over looked some small crack on a hose or bad seal around the intake. Just my thoughts. Peace, Jon

I will triple check this sometime next week....you are right, it almost does sound like a vaccum leak.

Thanks!
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL