I have a really bumpy idle at startup and it smooths out after a certain amount of time. it still has a slight vibration after this initial period but that is not my question.

what I want to know is why does the idle clear up like a switch is thrown in the computer. one second the idle is around 8-900 and is very stumbly and then it snaps out to a smooth 1500 which comes down to the normal 7-800 where it stays for the rest of the day.

the wierd thing is I think its something to do with the sensors or the computer because if I engauge the field service mode (jump A,B) when its rough it smooths right out until I take the jumper out or the engine warms up and it stays smooth.

I know it has nothing to do with open - closed loop because I can see this transition in field service mode and it does nothing to change the idle. only when I engage the FSM or wait for the engine to warm does the snap change occur.

WTF someone help.
its not CTS, knock or timing being off. I am in the process of changing the IAC and I just changed the plugs and wires. compression is great.

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88 WS6 T/A 305 TPI--
K&N,Air foil,hypertech chip, thermostat+fanswitch
free mods, dynomax catback, urethane motor+trans mounts, PST front end poly stuff, Earl's hyperflex brake lines SSM SFCs, Bilsteins very trick homemade ramair, Accel 300+ ignition system. Ported plenum, intake and heads with 1.94I valves.
Planning: Heddman 1-5/8 longtubes, NOS 150 plate, replace the "peanut"! and Eibach Sportlines.
check it out at:
http://www.geocities.com/transam617

 

I was told to never jumper the terminals while the car is running... Says right in the manual actually.... careful, you may blow the computer. You may have a stick IAC or some dirty vacuum passages in the TB.

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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

Sorry my friend you're wrong. In all OBD I cars, which would be ours, you enter "Field Service Mode" by jumping terminals A and B WHILE the engine is running. You're NOT supposed to start the car while A and B is jumpered but you CAN jumper A and B "while" the car is already running.


As for the original authors post... I believe it does in fact have something to do with open/closed loop. I just can't say what for sure. Check your IAC and your TPS both.


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1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

 

well I dont think it is open/ closed loop because I can watch this transition in field service mode and it doesnt change anything. what happens is I start the car and the idle is s**tty then if I immediately engauge FSM the idle clears right up. it does not immediatly go into closed loop however, that takes it about a minute or so as I watch the SES. I think when you engauge FSM you are bypassing one or more of the sensors or computer functions and this is what causes my idle problem. Now if I could only figure out which one.

by the way
its James

 

James in Springfield?? You move from FLA recently??

Anyhow, if it is you then use your scantool. Hook it up and watch the readings as the car warms up and goes from ****ty idle to clear idle. Watch your IAC counts and your TPS voltage. I'm guessing you'll notice some sort of something goin' on with one of those two.....

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1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

 

no not from springfield but I do wish I had a scanner -- thats for sure. I think Ill get one after christmas when I have the cash that would be the easy way to diagnose this little problem I am having.

[This message has been edited by 88305tpiT/A (edited November 25, 2001).]

 

Well sorry about that then. I'm meeting a guy up in Springfield tuesday that has a scanner and a thirdgen. When you said it was James I got confused because that's this guy's name too.

Yeah, a scanner would sure come in handy. I'm using this guys scanner for now until I can get my own. Luckily we have an Fbody board specifically for our state and lots of guys from my area go there. Real handy indeed.


------------------
1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.