Been having this problem for a little while, cant seem to figure it out, and now she failed my state emissions test. Car runs fine when engine is cold, soon as it warms up to around 200' or so, motor will have a lil bit of a rough idle, and rpms will jump from around 625-675 when the car is in gear...again..only when the motor is warmed up. Ive changed plugs, cap, rotor, wires, and checked for any vacume leaks..everything seems so be fine. One of my mechanics i know said to check out the pick-up coil under the distributor, and the distributor itself. By looking at the distributor, i am seeing that there is parts on the top of it that are rusty. The wires going into it on the backside seem fine with no fray marks or wear spots....anyone have any input on my problem? Should i try and put in another distributor??

 

yes, My V6 is having problems after warming up as well. However mine just dies out on me for no reason could our problems be related? It runs fine cold, but like urs around 200, mine stops.

 

Have you exhausted these possible causes?

Valve adjustment needed
Incorrect ignition timing,
Bad ignition wires (Test w/ ohmmeter)
Incorrect idle speed
Bad O2 sensor
Cold Start Injector always "ON"

 

dont know man, wish someone would chime in, cause my summer is tickin away...and i want my baby on the road....this problem is really annoying too...
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ive changed the wires, there brand new, dont even have 10 miles on them, idle speed when cold she idles right around 750 or so, which isnt to to bad, 02 sensor is new also, what is the cold start injector??..does my car have one??

 

If it's TPI it will -also it depends on year of actual manufactured

 

what does it do??...or its purpose?....its only when the motor is hot that the problem occurs, when shes cold it runs fine...a lil rough...but nothing super super serious

 

It's an electro magnetical solenoid valve that produces a very fine fuel spray that is supposed to run for only the first 7-8 seconds after ignition based on a thermal time switch if this is always on it could add fuel to the mix that throws off idle
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more or less... a "choke" for tpi

 

thats a great theory but what about my v6 EFI? Its got a very similar problem.

 

Fuel pump or relay may be a possibility if all the other possible causes are eliminated... it's definitely not the first thing to be checked in that case

or maybe an isc motor failure

 

well the hell of it is that the other day i drove it to blockbuster and coming back it did that thing where it stopped while idling. And then when i got back to my house it idled perfectly in gear reving and everything. thats the craziest part of all! so it CAN run while warm and it CAN idle, but sometimes it doesnt. GRRR

 

It definitely could be a fuel pump dying under acceleration like that normally id say timing if it was like that out of a cold start but the problem is intermittent but it may well be something else it's hard to say without seeing it you know thats the only downside to an otherwise useful forum
If you were going to check the fuel pump I would highly reccomend doing something that will make this a lot easier on you ( I am assuming this is an fbody) Instead of approaching the pump from underneath real PITA I would pull up the carpet under the hatch and cut your self a rectangular hole and fabricate in a simple access door for the pump out of some sheet metal and a simple bracket or something like that... either that or try installing an inline fuel pump a little more involved but easier access... basically you would need to go about it in such away that you can continue to test and adjust... I pray for your sake that it is not a timing chain beginning to fail because that condition also displays those symptoms you mentioned

 

get a timing light and check your timing while the engine is behaving oddly

I had a similar problem on a '91 it ran rough but ok'ish in open loop (cold) but when it went to closed loop it was a mess. Very unpredictable.

Turned out ot be the distributor HW need replacing. When checking the timing you could see it was moving around from -20 degrees to +60 degrees hence the erratic behaviour -- the ECM was just trying to deal with the fried distributor which resulted in very poor driving characteristics.

 

+60? You mean +6? I don't think +60 is even measurable. You are right that he should get a timing light and check the timing. I've never regretted buying any diagnostic tools. Also, you will need a timing light if you want to properly set your timing if you do replace your distributor.

Some people have mentioned fuel pump, but they usually don't cause rough idle when they are dying. Its higher throttle performance thats hindered.

I had a similar problem once and it turned out that two of my fuel injectors were bad. The problem was worse in closed loop because the 02 sensor was picking up all the excess oxygen from the two cylinders that were not firing, thus dumping WAY too much fuel to the cylinders that had working injectors.

To test for this first establish that you have a misfire. You can test for misfire by pulling wires for each cylinder off of the distributor cap (with insulated pliers/gloves) one at a time with the engine running and seeing if your RPMs dont drop (you can either buy an under the hood RPM gauge or listen for it if you are good enough). If they don't, then that cylinder is misfiring. Also a misfire will cause a puff of air out of the tailpipe along with a kind of "puh" sound. Once you establish a misfire test the resistance of the injector(s) of the misfiring cylinders and compare to the good ones. If they are lower by more than a few ohms then you have found your problem.

 

I 2nd that on the injector testing. If you have Multecs they should be removed and destroyed on principle.

I had both problems, injectors and distributor. The injectors were multec and garbage that they are had the usual problems with windings eaten through and shorting out. The other problem was with the internals to the distributor and yes it was moving from +60 to -10 and so on thats why it needed to be replaced. The GM dealer charged me $95 an hour for the diagnostics and in total the repairs cost $1100 I am not prone to forget that experience anytime soon

Eventually I replaced the distributor and the injectors and the problem went away.