'93 chevy lumina 3.1 MFI idle/running problems

[EAGLESFAN]

My '93 chevy lumina (120k miles) has an intermittent ignition problem. Coil pack, wires, and plugs recently replaced. What happens is most of the time the car runs perfectly fine but on some occations the car has a hard time starting then, when finally stared after several tries and flooring the gas pedal, the engine runs poorly and when accelerating from stop, engine hesitates then picks up. There is a huge loss of power and sometimes the smell of raw gas is noticed, like the engine is being flooded. My best guess is the Engine Control Module (ECM) which is what im probably going to replace soon. I also am going to clean the throttle body and remove the injectors and have them professionally cleaned and pressure tested, then reinstall with all new o-rings (of course). Other then that is there any other suggestions or similar incidences? What was done to solve the problem?

I also notice rough shifting or hesitation to shift around 50 mph with my automatic transmission. Any suggestions what I can do to prevent this from worsening or damaging the transmission further?

Any replies are greatly appreciated.

[Kooterskkar]

Might be a faulty throttle position sensor or crankshaft sensor. Does your service engine light cut on?
As for the transmission, change the fluid and filter. That usullay helps with alot of tranny related problems.

[300+]

What about temp sensor reading low causing too rich a mixture. Or poor connection causing intermittent reading. Usually wont start if temp sensor disconnected. (if warm out)

[Kooterskkar]

Might check the vacuum lines and the feul pressure regulator too.

[EAGLESFAN]

Well I just replaced the ECU because someone told me that is usually the source with this intermittent type of problem. I've only driven the car about 40 miles since it's been replaced, but so far everything seems normal (except of course the engine running rough a little while the ECU tunes itself). The check engine light never came on even before I changed the ECU. The vaccum lines seem alright and the car holds good vaccum. I guess the only way to find out whether the problem is solved is time. I thank all of you for your imputs. I'll post another reply in a few weeks indicating whether the problem has returned or not. Thanks!

[jeffcoslacker]

Mass air flow (MAF), the one in the duct from the air cleaner to the intake has been known to do this. When it malfuctions, the ECM cannot determine volume of air entering the motor, and so cannot meter fuel properly. If you catch it in the act, tap lightly on the sensor body, with a plastic screwdriver handle or something like that, and see if it clears up. Conversely, you can tap on it when its running fine and see if the motor begins to break up as you do it. If so, you've found your problem.

[quattro527]

Originally Posted by EAGLESFAN

Well I just replaced the ECU because someone told me that is usually the source with this intermittent type of problem. I've only driven the car about 40 miles since it's been replaced, but so far everything seems normal (except of course the engine running rough a little while the ECU tunes itself). The check engine light never came on even before I changed the ECU. The vaccum lines seem alright and the car holds good vaccum. I guess the only way to find out whether the problem is solved is time. I thank all of you for your imputs. I'll post another reply in a few weeks indicating whether the problem has returned or not. Thanks!

Bump... Seem to be experiencing the same issue here. The car would sometimes need to be cranked a good 10-15sec, and would immediately stall if you dont give it any gas. I have to give it some gas and hold it down for a few seconds, and then let off, and the idle would sometimes stablize. However, the idle would still be very rough... and the car would sometimes stall when stopped in traffic. Lower-rpm power band is also very rough, as if the car was missfiring, then go back to normal up top.

I've replaced at this moment just a set of sparkplugs, which helped just a bit, but didnt cure the problem. The plugs came out scorched black from excess carbon fouling (running super rich).

OBD-II scan did NOT pull up any codes either. Wondering if anyone else has had this problem and found a solution for this before I go out spending hundreds replacing components (MAF, EGR, Ignition Coil, etc) that has no guarantee of fixing the problem.

The car is a 3.1li 98 Lumina with 115k.

Thanks