Just completed a Super Ram install on my 86. Also installed a new TPiS 58mm TB and Alvin pcmforless chip and have the following idle problems:

1. When cold, the idle is so erratic (jumps between 600 & 1400 RPM) the car dies at the bottom of the spike.

2. Once warmed up, the idle is fine when you start the car but while driving, the engine will die when you depress the clutch (i.e. slowing at a stop sign). Once stopped, if you start the engine it will idle fine.

I have properly set the TPS, IAC and minimum idle to specifications. Would raising the minimum idle setting help? Any comments would be appreciated.

 

I have had an idle problem since I put my motor in. The engine was complete from LPE. I'm not knocking LPE in anyway I love them and the engine and I will deal with this problem if I never get it fixed.

Kinda have the same similar problem. Low idle then dies, then other times it's fine. It's really a PITA to drive when you have to press in the clutch and hit the brake and the gas at the sametime. Last time I looked I only have 2 feet.

Did you use a gasket when sealing up the SR or silicon?

 

Regarding the erratic cold start:

It is difficult to get the right balance between start-up fuel enrichment vs coolant temp, open loop fuel vs coolant temp. spark advance and desired idle rpm vs coolant temp to get a stable idle right from start-up through warm-up. Expect lots of fine tuning in these areas to get it right.

Regarding stalling:
Stalling with the clutch disengaged while rolling is likely a mismatch between the min air and the warm IAC park position vs. coolant temp table. Not enough air!

Either the min air is insufficient or the warm IAC park position vs coolant temp table is permitting the IAC to close too far. This needs to be tuned to match the car's demand for air at idle vs coolant temperature.

A short term fix would be to increase the min air to something close or equal to your normal desired warm idle rpm, that way the IAC can't reduce the air to the point of stalling. It helps if you know the desired idle rpm to set the min air appropriately.

If you increase the min air, be sure to set the tps back where it belongs, or the warm IAC park position table will hold the rpm up in a stationary idle.

I see you have an 86 4+3. FYI: we recently hacked an 88 bin to work specifically for 86 4+3 cars. See this thread for more details:

http://forums.corvetteforum.com/show....php?t=1753750

 

Quote:

If you increase the min air, be sure to set the tps back where it belongs, or the warm IAC park position table will hold the rpm up in a stationary idle.

I didn't reset the IAC after setting the min air. That could be part of the problem?

 

Tequila, what exactly means the table warm IAC park position vs coolant temp ?
i know my car NEEDS (before to enter in closed loop) MORE air to stay alive when started.
In this table (untouched) I have ridicoulous values of IAC steps for the needs of my car programmed to idle at 900 (warm) and about 1100 when started (Idle Engine speed vs. temp).
The table warm IAC park position vs coolant tempis the first table the calibration follow before to see the Idle Engine speed vs. temp?
If I start the car and the coolant is 56°C the table warm IAC park position vs coolant temp is saying 25 steps.
AT the same temp the Idle Engine speed vs. temp is asking 1000 rpm that are impossible to maintain with only 25 steps..(at least in my car)
Please share your knowledge.
-Beppe-

 

As I understand it, the Warm IAC park position vs coolant temp table is in use outside of the norm closed loop PID idle control desired idle rpm vs coolant temp table (not to be confused with closed loop fuel control) and when the IAC is not really in throttle follower mode (low tps voltage). It is sort of a fall back position when the controller really doesn't know what it should be doing between modes.

Likely conditions for the warm IAC park position table to come into play:

Vehicle speed > 1.8 mph and off throttle or very low throttle opening (before tps begins to add IAC counts in throttle follower mode), or mis-adjusted tps sensor (voltage too high).

I use this table to tune my car's rpm/speed for rolling in gear at idle. I like to idle in 2nd gear at 8 mph down my dirt road, so I've tuned the warm values of this table accordingly.

Also I have an issue with my speedometer that causes false readings when stopped, due to battery relocation cable routing RFI issues. When my speedometer starts to dance when stationary, the Warm IAC park position takes over the idle control.

Because of this, I try to match the tune of the Warm IAC park position vs coolant temp table to be very close in value to the values obtained when in normal closed loop PID idle control at the same coolant temperatures.

Tuned in this manner, I still get a reasonable idle even if my speedometer is going haywire. I know, I need to correct for the RFI issue, but this was easier than re-routing my battery cables again.

I recommend tuning this table to closely match the cars normal IAC counts vs coolant temperature (maybe slightly less so the car will still coast down off throttle at speed, If set too high, the car will tend to sail on after lifting the throttle making it harder on the brakes etc.).

You just have to figure out what is normal for your car at a given coolant temperature given its min air setting and demand for air at the desired rpm for a given coolant temperature.

 

I had the same problem when I installed my SR. I had a vacuum leak. I also put in a custom Fastchip. It runs great now. No codes and a steady idle. But I still have a stock cam. I wonder if a 58mm TB is too large. I was told that a 52 was good for a slightly modified L98. You may need a 58 MM TB.

 

I was told the 58mm won't improve, but also wouldn't be detrimental to perpormance. I wanted a quality billet aluminum TB and TPIS doesn't manufacture a 52mm in billet AL.

 

Thank you Tequila!
I'll try to play with these tables..
-Beppe-