I am helping a friend with his LT1 94 TA A4 and the idle goes up and down between 1200 and 500 rpms and dies, but runs awesome above idle all the way through the power band and not throwing any codes, unless maf is unplugged but goes away once you hook it back up?

Here is the list of parts that was thrown at it to fix the problem
IAC
TPS (.64 idle 4.55 WOT)
Temp sensor (The one in the WP)
Maf Sensor
O2's with extentions (direct plug in not the wire and butt connectors)

There is no vacuum leaks and fuel pressure holds steady at 39-38 at idle and goes to 43 at WOT or by unhooking the vacuum line to the FPR.

The car has a cc503 cam (with all valve train upgrades for the cam), 1.6 RR, LT headers, true duals, egr and ac deleted and the PCM was tuned by Madtuner.com (idle set at 800 in P/N and 750 in gear with) with stock every thing else and the problem was there before the tune was done. It was idling fine with out the MAF at first so that is what made me think MAF was bad but after the new one was installed the problem is still there.

Havent got a clue why it does what it does need help.

Thanks in advance

 

Bump

 

Is the fuel pressure regulator stock?

 

Is the MAF reading fairly steadily if you do get the engine to hold a steady rpm??

Seen MAF wiring get messed up a few times.

 

Yes it is.

 

I will have to check that, thanks.

 

Well we hooked up the scanner to it today and it actually had five stored codes that weren't in there before.

16 18 36 41 which as far as I can tell are all pointing to the opti.

And there was also 48 which was the MAF not sending a signal but I am sure thats when we were unplugging it while it was running while trouble shooting.

LT BLM was at 18 while at idle and the MAP was at 13 iHG and the MAF 16.1gls, but when the car was not running it was showing 45 rpms.

So I am thinking opti what do you guys think, is the opti bad or is there something making the opti have a false reading (connections are good)?

 

DTC 18 is a fuel injector circuit fault, and has nothing to do with the Opti.

DTC 41 indicates an "open" in the ignition control module circuit. Not necessarily related to the Opti.

The other two are specific codes for the optical sensor in the Opti. Could be as simple as bad corrosion or pin damage in the two Opti harness connectors. Check them both out. Clear the codes, and see how fast they come back. DTC 16 for the low resolution pulse pattern isn't unusual to find as a "stored" code. If the engine it running, it has to be a stored code, because if its an active code, the PCM shuts down the fuel system. I think DTC 16 sets at times when the PCM has trouble finding the low res pulse on startup. DTC 36 for the high res pulse signal, unusual to find. It can be an active code and the engine will still run, but with a minor loss in spark timing accuracy.

Both pulse signals are used by the PCM to determine RPM, and if you have an erratic RPM signal from the optical sensor, the PCM isn't going to be able to control the idle RPM correctly. You're on the right track, but may have a couple problems besides the Opti.

Your other data appear to be jumbled. "18" is the BLM cell #, and that should be 16 at idle. 18 is the open loop control cell, when the engine is not at idle or under load. That problem is typically caused by the TPS being above 1.0V. MAP of 13"Hg is good for the 503 cam. The 16.1 gps MAF reading is higher than normal for idle, and would indicate the throttle is partly open, not closed. Its normal for the data log to show a non-0 value for RPM when the engine is not running.

 

We did have to have the throttle partially open in order for it to run. What would cause being faulty could cause all of these codes?

 

First clear the codes and see how fast them come back. Pull the "PCM BAT" fuse for 30 seconds. If the codes don't come back, it was an intermittent problem, which may pop up again. If they come back immediately, you have to chase down the source of the problems.

The injector code indicates one or more of the injectors is not working correctly. Could be a faulty injector, could be faulty wiring. Put a 'noid light on each of the injectors and verufy that the PCM is supplying the ground required to fire the injector. Verify you have 12V to the pink wire on each injector harness connector. Measure the resistance of each injector to see if it is in the range of 12-15 ohms.

The IC code indicates a problem with the IC Module or the wiring. May relate to the Opti. There is a diagnostic logic chart in the factoryh manual that will walk you through diagnosing DTC 41.

The two Opti codes are due to a faulty signal from the optical sensor in the Opti. The signals, at some point in time, are not reaching the PCM. You have to figure out why... either faulty optical sensor, or faulty wiring. Check the harness connectors first, as I indicated already.

 

Cool, thanks for the direction thats what I was looking for.