Knight94

Well here is an issue I have been dealing with for awhile now. I also have been doing some prom tuning to this to no avail yet.

But I am posting this in the TPI section because right now I am using my stock prom. My car is 88 Firebird. Motor is slightly modified. 350 bored to 355, Edelbrock Performer Heads and High Flo Intake. Edlebrock Headers. Comp Cams Camshaft. 1.52 rockers. Motor was completely rebuilt with all new sensors, because I swapped motors. This motor does not have the cold start injector. 24lb Bosch III injectors.

Anyway, when I startup the car (cold start) it idles great! Open loop works great with no problems. My car idles at 700 in Park and 650 in Drive. When it warms up it and goes into closed loop it idles fine for a while. Then certain criteria must be met for the idle hunting to begin.

If I start the motor from a cold start and just let it idle to warm up temps (no throttle at all) it idles perfect even in closed loop. But when the fan kicks on it will really lightly start to idle hunt. from 600 to 800rpms. And after a min or so it will idle correctly with the fan still running. No idle change when the fan turns off. Now here is the kicker, It doesn't do this all the time. Probably 3 out of 4 times though.

Also after I have been out for a drive and parked it. Restarted while still warm. After the short open loop startup (which is fine) is switches to closed loop and starts to idle hunt. Takes a minute or two to settle down and idles fine. When it is idle hunting the WB O2 sensor will bounce from 17ish (low rpm) to 12 or 13 (high rpm). When at a steady idle my WB reads 14.3 to 15.3.

Now this only happens when I have the car parked. When I am driving or idling in drive,. I have absolutely no idle issues or hesitation. In fact, while the car is idle hunting (in park) if I put the car in drive (no feathering the throttle at all) it will stop the idle hunting.

Now I have been all over the web and this site looking for help on this topic. I did all the obvious tests. Timing : 6* IAC : Pulled and cleaned ( also verified by changing to another known good IAC) TPS : .53 (also verified by changing to another known good TPS) Pulled and cleaned the throttle body. MAF tested with meter and also with another known good one. Vacuum leaks : Put new vacuum hoses on when I swapped motor (couple years ago). Also checked intake area and hoses with the DYI carb spray technique: none found.

Now if I disconnect the EST connector. Idle Hunting stops. don't know if that puts it back in open loop mode or not. But like I stated, I have no problem with it in Open Loop.


So any ideas????? If someone thinks this might be a tuning issue, please let me know and I will repost this over there.

Thanks