Hi guys,
I’m running a 350 tbi with a comp cams CL 12-256-4, full exhaust, salad bowl, 1” tbi spacer, fuel psi @ 18lbs with an AFPR. I’ve put this project off for quite some time but now have the time for it again. However, I’ve run into some idling issues I can’t seem to solve.

Cold startup just can’t be done without using the pedal. It turns over and dies instantly. I haven’t touched the stock commanded AFR for it.

The bigger issue is that when in gear and at 0% throttle, the engine pulls itself to 8-9mph. At the stop light the IAC is at 100 steps and continues to climb to around 120ish. You can actually feel the engine fight against the brakes. When I shift back to park, the engine shoots up to 1800rpms at 137 steps. This is in open loop and the AFR read at 13.6. At 0% throttle the tps reads .5v. Im not sure if this a vacuum leak or tune related but it’s hurting drivability and needs to get sorted. I appreciate any help here fellas.

 

Has the BPC vs VAC table been adjusted for the higher fuel pressure?

What are the park and in drive idle speeds set for in the BIN?

Grab a data log and look through it, at a stop is the ECM in idle mode? What is the engine RPM? Engine coolant temperature? IAC step count? If the idle is higher then the desired (from the tables), is the ECM stepping the IAC closed?

RBob.

 

Yes BPC has been adjusted and and it is at 116.

Park idle speed for this datalog was 1000 and drive was 975. (Maybe relevant but now i have dropped it by 100 for both but havent tested)

Engine does go into idle mode at a stop. In drive it idled at 950rpm 114 IAC steps, then started to fluctuate 937-981rpm as IAC steps went up to 122. Coolant stays around 180-185. WB reads around 13.9 and cAFR is 13.5. KPA is 53 and SA is 23*.

 

OK, off to a good start.

Why so high, with that cam shouldn't need to be much above 650 RPM idle speed. A little more in P/N, say 700 RPM. This is why it is pulling through the brakes at a stop, the convertor is starting to engage.

Then the ECM is controlling the idle. One problem is that the IAC counts are too high. This is the main reason for the starting issues. On a warm engine, in P/N, and no other loads the IAC step count should be 5 - 10 steps. Can adjust the idle stop screw to achieve this.

Although i would first lower the desired idle speed.

Once the idle is better, can adjust the IAC - Park to Drive steps parameter to get a better transition between P/N and drive.

RBob.

 

Thank you so much, the lower idle fixed the converter issue and the cold start issue.

IAC steps at a warmed up idle are now 30, much closer to that 5-10 that will come with the idle screw. Thanks a lot, can't believe it was something that simple

Thanks again, driving her is fun again.

 

Thanks for getting back to us. This will help others. Enjoy the ride and don't be afraid to chime in.

RBob.