Good idle at time then bad others, what the hell?

[Jon89le]

My cars been starting fine but this is the second time its done it in about 3 weeks. Ill try to start the car and it'll have a real hard starting. Like its choking. This time I had to start it and while the motor was trying to turn over, hit the gas and once it fully started, rev it quick (up to like 3k nothing crazy) to keep it alive and then it went away. I even shut the car off for a bit and it started again fine. The first time it did it id do the exact same thing but once i let go of the gas the car would idle bad. It did this for about 2days. And the first time i smelt gas in the exhaust like it was just burning gas. This second time i just smelt it faintly. Any ideas what this could be? IAT, MAP, coils? Any help is appreciated

 

Also: no check engine light comes on...

[Redfox340]

I'd pull and check all of the spark plugs, if your smelling non-combusted gas it's sounds like you're not completely burning from either a) faulty plugs, faulty wire(s), or c) a possible ignition coil. But, remember this is from a first glance at it. You know what's been change; fill us in what's been done recently... the more we know the better! Best of luck!

 

- RedFox340

[Brian P]

My vote is for a bad coil

[Jon89le]

Doesnt a coil just go bad? how would that explain the problem coming and going?

[Robby1870]

would the IAC cause the prob?? The MAP will send a code, the IAT will send a code also, so, plugs and wires and coils are your best bet

[chronic139]

the car can run with one bad coil. the two cylinders that it controls just dont fire. Ladies and Gentlemen we have a four cylinder!

[DOHCRagtopguy]

Throttle Position Sensor?

[Jon89le]

Im pretty sure all 6 are firing since its got balls when i drive it. Theres a new TPS in there. And i also have brand new Rapidfires in there as well as brand new 8.5mm Magnecore wires.

[BlueCutSupreme]

yeha i'm havign a very similar problem, mine will sometimes just shut off when i am slowing down too, other days it will drive perfect.

http://www.w-body.com/forum/viewtopic.php?t=2446&highlight=

[Robby1870]

that random dying could be the crank sensor. That happened to me. I couldnt diagnose the problem because it was random.

 

Robby

[88Intl]

Cleaning the crud off the idle air control valve and throttle body couldn't hurt. I did this on my 2.8 and the idle is very consistent now. Used to stall when backing up then braking, but no more. This page is written for Z24s, but I used it for my Cutlass:

 

http://www.v6z24.com/mods/howto/?page=throttlebody

 

Last time I disconnected and reconnected the battery I skipped the IAC position relearn, and it still idles fine. Maybe the default settings are OK when everything is clean?

 

http://www.sts.sae.org/membersonly/techinfo/articles/article7.htm

 

When B+ is disconnected on 1987 and newer 2.8, 3.1, and 3.4 engines, the ECM loses track of the IAC value position and the engine will usually not idle properly. The IAC position must be re-learned............

 

With key off, disconnect battery for at least 30 seconds.

Reconnect battery. Do not touch throttle (ECM looks for 0% throttle openings).

Start the engine and shift to “D.†Run for ten minutes or until cooling fan cycles.

Shut off engine. Wait 30 seconds.

Restart. Run 5 minutes in “D†or until cooling fan cycles.

Check idle speed. (Note: the ECM can only learn eight IAC counts per key cycle).

Repeat procedure if not correct.

Remember that when the throttle opening is less than 2% (2.8) or 5% (3.1), fuel delivery is based on IAC counts. Correct IAC position is critical to prevent stalling. Normal is about 15 counts.

[gimp19]

Sounds exactly like the problem my car was having a month ago I think\hope it was just bad/frozen gas. Cause it was about 5degrees and I had less then a 1/4 tank the car has only acted up once since I filled the tank and put some winter gas treatment in.