Has anyone else been having this problem? Whenever I shift my car from any gear to Park or Nuetral the engine will rev up to around 1600 rpm, and then drop back to my idle speed of 750. I can't figure out where it's coming from. I'm assuming it's in the PROM somewhere, cause I've eliminated everything else (that I can think of anyway). IAC is brand new, passages are clean, IAC, min air and TPS are all set correctly.

If anyone has any input I would appreciate it.

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Black 88 GTA L98
261 RWHP, 345 RWTQ
13.406 @ 103.72 MPH
ZZ4 bottom end, Edelbrock 6085 heads, LT4 HOT cam, GMPP 1.6 RR's, ported stock TPI, SLP 1 3/4" headers, no cat, Dynomax cat-back, Stock PROM
E.T.F.A Treasurer

 

Anybody?

 

There is a "RPM add for Park/Neutral" constant that defaults to 100 rpm. But this is the "steady" rpm and will "flair" up when you shift. Try lowering the setting and see if you like it. I have one friend with MAF that runs 0 and he much prefers it. There still seems to be a bit of a "flair", but nothing noticeable. I personally add "13" rpm on my SD car and I much prefer that setting. It eliminates any "drivetrain" shock that I use to get when shifting from Park/Neutral OR Reverse-Drive, since Neutral is in between.

Experiment to see what you prefer. Everyone has a personal preference.

 

Both the P/N and A/C adders are currently set to zero. I like to add a few rpms there myself too, but I zeroed them to see if it was the cause. But it didn't change anything.

I can't figure out what's causing this. It really just seems like the IAC can't react enough to the load change to maintain a steady rpm, but I doubt that's the fact.

 

I've got the same problem, but can't try to fix, because I dropped my laptop and destroyed. As soon as I get a new laptop, I'll try what has been mentioned and see if it'll fix mine.

Sparks a flyin'

 

arrrghhhh..... ^ sounds all too familiar.... Being laptop-less blows goats........

I feel your pain, bro.......

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

I've still got the same problem with a friend's 88 IROC. The "add to idle" is 25 RPMs, I was going to try raising it to 50 or 75. The car will stall when its cold/open loop when going from park to reverse or drive. When its warm it will raise in RPMs as you describe.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Well, looks like I'm going to have to figure this out myself. I'll let you guys know if I find the cause.

 

Here's how I look at it. The idle speed vs. coolant temp table is for when the tranny is in Drive (automatic cars only). The P/N idle speed constant is added to the idle speed being requested by that table. Now, when you go from Park or Neutral to Drive (or Reverse), you're putting a load on the engine, so the IAC motor needs to open up. However, if you're requesting a 100 rpm difference, the change in load would be less than a 0 rpm difference between P/N and Drive, so the IAC motor won't have to move as far to stabilize the idle.

What Scott 88 GTA is seeing is the opposite when shifting from Drive to P/N, where the load is being removed from the engine, so the engine speeds up and the IAC needs a little time to compensate. To keep the IAC position the same between Drive and P/N, you'll want to increase the P/N adder constant. Mine is at 150 rpm and the IAC barely moves when shifting between P/N and Drive. With a higher-stall converter, there is less of a load on the engine in Drive, so you can get by with less of an adder. With a bigger cam, the engine also responds differently between P/N and Drive, so you may need a larger P/N adder.

Kevin, you'll want to increase the P/N adder to make the IAC motor extend more in P/N, so that when he shifts into Drive, the IAC is already opened up more and therefore flowing more air through it. So, instead of dropping from 775 to 750 rpm and the IAC having to increase by 50+ counts (just a guess), he could drop from 825 to 750 rpm and only have the IAC increase by 5-10 counts or even less.

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Greg Westphal
'87 IROC 355TPI/A4

 

I honestly don't think you will ever entirely eliminate it. My SD car has a very mininal fuel add for P/N. And I have even tried it at zero. There is ALWAYS a little "flair" in the RPM when I shift from Drive/Reverse to Park/Neutral.

I have looked at my Fuel Tables and compared it to the Kpa readings of my engine when I am in Drive and Park/Neutral. My Kpas in Drive is roughly 40 kpa, while in Park/Neutral it is 30 kpa. To maintain the proper BLMs, I have a slightly higher fuel for 600-800 rpm @ 40 Kpa vs 30 Kpa.

I have not tried setting all the fuel values for 40 and 30 kpa the same, but I honestly don't expect that to fix the problem. The engine is going from a situation where it has a load on the engine to no load. The moment you take the engine out of Drive and put it in Park/Neutral, you remove the load while the engine which takes the ECM a moment to react to (the ECM is fast, but not instantaneously). So you get this momentary flair of a couple hundred RPM, since the load has been removed and then it settles down to the no load in Park/Neutral.

It is the same if you carefully observe what happens when you take the transmission from Park/Neutral and put it in gear. There is a momentary point where the RPMs drop below your Desired Idle Speed, but when the ECM catches up, it settles down. But it does momentarily drop when you put it in gear.

If the "flair" is greater than a couple of hundred RPM, then you do need to do a little work on your "idle area". Look at your Spark vs LV8.

Also, look at your LV8 readings and your Air Flow readings when you are in gear and when you are in Park/Neutral. Some tweaking in this area may bring the flair to more acceptable levels. But don't expect to totally eliminate it.

 

I'm not expecting to totally eliminate it, but my "flair" right now is about 900 rpm. That's ridiculous. I hadn't thought about looking at the LV8 readings. I'll do that tonight.

 

Greg, I made that post and then headed off to work. I didn't realize that you had made a similar post regarding "engine load" as I had.

You make an excellent point about the IAC and possibly that is why my "flair" is so minimal. I added a table to my $8D called "Idle Speed IAC Steps Vs Coolant". This table is different than the "Idle Steps Vs Coolant" (as it's called SD or "Warm IAC Park (steps) Vs Coolant" as it is called in MAF.

The "Idle Steps Vs Coolant" is the maximum number of steps the IAC is allowed to make when Idling (as I understand it). The "Idle Speed IAC Steps Vs. Coolant", which I added to my SD TDF is the actual default position of the IAC at various coolant temps.

In my tuning, I did a lot of work on my idle and setting the IAC Position in the "Idle Speed IAC Steps Vs. Coolant" based on my Diacom readings. Possibly due to my tighness on this table is one reason my "flair" is also so small compared to what others are experiencing. I am quite sure a similar table exists in the $6E, but it just hasn't been defined in TunerCat (yet).

PS: I think it is a shame some of these tables are named so similarly. They should call one "IAC Position @ Idle vs Coolant" and the other "Max IAC Steps vs Coolant". I will look later tonight to see if I can find where the "IAC Position @ Idle Vs Coolant" table is within the 6E (or a similar table).

But, I think a little more tweaking with these two tables (getting the position more accurate and possibly reducing the number of steps permitted) might help minimize the "flair".