Professional Engine Builders and Tuners – Engine Idle Help Needed

[MarcSpaz]

I am sorry for the long post, but I really need some help. Here is the problem that I need help with…

My car was running really well. I made a set of delete plates, went to get the car tuned, and installed the plates on the car at the tuners. The car went crazy or got stupid; I’m not sure which. After the tuner made 6 or 7 attempts to tweak the car, I lost 20 RWHP, 27 RWTQ, and the car has major idle problems. Even at 1200 RPMs it has an idle hunt problem so bad that it almost stalls 3 or 4 times before it levels off, and it does stall on occasion. It is also hard to start, both hot and cold. When I have the AC on, it actually stalls between gear shifts, and I have to pop the clutch to start it again.

The person tuning my car eventually gave up, thinking the car has mechanical problems, possibly relating to unmetered air. Especially since the dashpot was bumped 30% and commanded changes to the idle seemed to make no difference in how the car ran.

I, however, am not convinced it is a mechanical problem for several reasons, and I need some direction on what to look at. Here’s why… I was out of town at the time and needed to get the car home. I drove the car for about 100 city miles (afraid to take it on the highway), made no changes whatsoever, and the car magically started running fine, literally while we were driving.

I got home, car still running fine, and put it on a dyno here. Even though the idle issue was completely gone, the unexplained power loss was still an issue. I know it is not dyno variances, as the car pulled the same HP and TQ on both dynos within one half HP/lbs of each other. I also I made some minor changes and reloaded the tune and the idle hunt issue came back just like day one.

I pulled the homemade delete plates off, put the stock charge motion plates back on and dump the old tune in. I picked up about 7 RWHP and 18 RWTQ (still not where I expected it), but the car still had the same idle and stalling issue as before. After about 3 or 4 hours of drive time, it seems like the computer just leveled itself out again and the car started running fine. The next day, after a great test ride, I dump the same tune back in completely unchanged, and the idle went to hell again. Then, just like the days before, worked itself out after a few hours of driving.

I started the car, let it idle, and sprayed brake clean on every seam and crack from the MAFS joint on the intake elbow to the base of the heads and there was zero variance in the idle.

Another caveat, this is not a new problem. I have had an idle-hunt problem after a flash with every tune I have ever had. I think it is as bad as it is now due to the airflow mods I have, as I have watched this problem get worse as I modded the car more.

I am going to by an X-Cal 3 and have a local shop help me out with a tune, but I don’t want to spend $400 for an xcal and $300-$500 for a tune to find that it is a hardware issue.

So what the hell do I do from here? How do I test for potential mechanical issues vs. tuning issues? Have any of you had idle problems like this, or cars that did not respond to changes commanded dashpot settings?

Thanks in advance,
Spaz

[ArtQ]

Marc, have you datalogged your short term fuel trim?

[MarcSpaz]

Only during the dyno pulls. Should I hook up the laptop and go for a ride? What would I be looking for?

[ArtQ]

Short terms ideally should be no more than +/- 5 %. See what your running under differnet conditions. If your short terms are working too hard (more than +/- 5%) to maintain stoich your fuel mapping may be off. Being that a pro tuner is invovled I doubt it's a mapping problem. However this a good way to see if there is a problem.

Short term fuel trim is only active in closed loop. It's an ask, give/take, check and ask relationship.

[MarcSpaz]

Well, the steps noted below fixed the idle problem. It came from my owners manual. I had no idea this needed to be done. Someone from another forum pointed it out to me.

I can only assume the 13 hp and 9 lbs tq lost are due to weather diff's between early March and the dead heat of summer.

I also clean the TB and MAFS anyway after I confirmed the above mentioned process fixed the problem.

Thanks for all of your help...


<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Because your vehicle’s engine is electronically controlled by a computer,
some control conditions are maintained by power from the battery. When
the battery is disconnected or a new battery is installed, the engine must
relearn its idle and fuel trim strategy for optimum driveability and
performance. To begin this process:
1. With the vehicle at a complete stop, set the parking brake.
2. Put the gearshift in P (Park) (automatic transmission) or the neutral
position (manual transmission), turn off all accessories and start the
engine.
3. Run the engine until it reaches normal operating temperature.
4. Allow the engine to idle for at least one minute.
5. Turn the A/C on and allow the engine to idle for at least one minute.
6. Drive the vehicle to complete the relearning process.



The vehicle may need to be driven 10 miles (16 km) or more to relearn the idle and fuel trim strategy.



If you do not allow the engine to relearn its idle trim, the idle quality of your vehicle may be adversely affected until the idle trim is eventually relearned.

</TD></TR></TBODY></TABLE>

[chad05gt]

Man, that scares the shit out of me... alot of people having trouble w/ strokers, big bores, etc...

Im sticking w/ 281 w/ my bottom end... just seems risky.

Mark, btw, how did bigger MAS test go???

[MarcSpaz]

Man, that scares the shit out of me... alot of people having trouble w/ strokers, big bores, etc...

Im sticking w/ 281 w/ my bottom end... just seems risky.

Mark, btw, how did bigger MAS test go???

It' didn't. I'll send you a PM.