Ok, now my car is still screwed up. It has been stumbling on occasion and has now started idling really low sometimes and then will go up to 1800 or so sometimes and stay there. I thought TPS? I checked it and had about .55 volts at idle(not running) and about 4.5 or something at WOT. That seems fine but I'm wondering if it could be going "haywire" sometimes at causing this SH$#. What do you guys think? THX very much!! Also, no codes at this time and it runs AWESOME most the time.
P.S.- I'm swapping for my other L98 soon and would like the TPI in good working order. THX again!

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'91 GTA:5.0TPI-5-spd, Hypertech Stage 2 chip, 160stat,!TB,!Cat, K&N, Flowmaster muffler, Accel Coil,TPI Air Foil, 1LE Alum DS, poly-tranny mount, KYB's all around, & a Hotchkis Strut tower brace.
Mods in progress:
-L98 w/ZZ4 cam/springs
-Edelbrock headers
-3" flow setup
Future:
-T56/heavier clutch
-Hurst or Ripper
-4.10's
-Ram Air II Hood
-1.5" Springs
-Rebuild suspension!
Others:
-39 Chevy coupe
350/350/3.55posi
-52 Chevy p/u
-77 Bonneville 400PONTIAC/400turbo/posi
Original 50k mile 2 door... Gramp's old car!
*** Gotta love those Poncho's***

 

Anyone? I'd like some help if possible. Its just really aggravating me!?!?!?!

 

Initial guess would be something amiss with the IAC Valve.

 

Yea, that and check for any vacuum leaks.

 

I swapped IAC's out of my other GTA and it still did it. Unless they both are bad? How do I check them? They both were ok on length. No more than 1-1/8" right? Well, I'm not sure what to think. I thought that the EGR was messed up too, but not too sure. My dad was messing with it and putting vacuum on it to see if was working. When he did it seemed to clear up, but then I don't know why it would idle up like that though? Maybe i have a combo of problems?

 

Anyone else? How do I check the IAC? THX


[This message has been edited by GTA91 (edited January 18, 2001).]

 

A weak MAP sensor will also cause this. Could be a flaky sensor or a vacuum leak. A scan tool would probably show if anything is amiss or irregular with the sensor readings.

BTW, I notice you have a 160* t-stat and the TB bypassed. Is it cold right now where you live? You are aware that a 160* t-stat and TB Bypass can cause the EGR to not function properly in cool temperatures just from 30-40*F?

Try swapping to a hotter T-stat and the stock eprom. The jet chip does basically nothing anyways, other than play with the #1 fan temperature and part of the mid range on the spark advance. I have the BIN, and there is very little difference between it and the stock GM eprom.

 

I should also add the a 160* T-stat and TB Bypass makes the ecm think it is permanently in "start-up mode" and it never gets to the proper settings. The ecm uses the difference between the MAT and CTS to let the ecm that while the T-stat might be at the correct temperature, it still has to add fuel...much more than you really need for the slightly cooler charge that is going into the engine.

The GM eprom algorithm never considered people would disconnect the coolant to the TB or relocate the MAT; and it works against you. And altering the tables is not a permanent answer (which none of the over-the-counter aftermarket chips touch anyway).

 

Actually I don't have the !TB done yet. I was going to but its cold here so I was reconsidering. I DO have the Hypertech though. NO I didn't waste my money on it... it was in it when I bought my car. Thanks for the help. Where can I get a scantool or borrow one from?

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

Hypetechs aren't a complete waste of money; most have a ZIF socket that you can use to swap a 27C258 eprom into...so they do have a useful purpose.

That aside, TPIS use to rent Diacom+ for $50/week and would convert the rental payments to a reduction of the purchase price if you liked it. Diacom+ runs on your computer. If you have a notebook or locate a used 286 or 386 notebook (they are dirt cheap because no one wants them), you can use that.

If you don't have access to a notebook or can't locate a cheap used 286 or 386 notebook, then look at Auto-xray. They are suppose to have improved it immensely according to the guys that have them and now have the capability of downloading to a compuer for the data. I think the Auto-xray is only setup for a single type of engine combo (not sure) but the Diacom+ works on every GM car from 82-95. You can buy an upgrade from Rinda to make it work on newer cars than 95s.