Don't give up on the cross-fire system yet. Check into some of the suggestions listed. (IAC and TPS)

I was just thinking of another item that could cause idle problems, since you mentioned that it runs fine til warmed up and then messes up after it sat for a few minutes.

This happened to a couple cars I've worked on. (Temperature sending unit.) Not the one that send a signal to the gauge. But the one that sends a signal to the ECM. If that is giving false temp. readings to the ECM it can mess the idle quality. Odd but I've seen this happen. 

Sarge

ok guys
well we have checked every thing you can think of on car.
(iac) motors were checked they are to be set at 51 they are at 52 . we did find a pluged vac line coming off of the pcv
not the big vac line but small line that goes to a polution
control box. (egr) valve also was pluged with black
electrical tape i ordered another (egr) valve .
i've changed temperature sending unit like sarge said still
won't idle we worked on car all afternoon on friday car had to run at least four hrs . as we worked on it it did idle a little better then had to go to bank before they closed on way to bank i ran out of gas.
                           


    mark82

It still sound like an IAC related problem.  In reality, 51 or 52 for a fully warmed engine is too high.  If you have numbers like that the IAC is compensating for another problem.  You cannot set this number.  The computer creates it based on conditions and required idle, provided the IAC is working correctly.

With a crossfire, a vacuum leak will make it run faster.  Vacuum leaks act like an open IAC.  With an IAC command of over 50 the car idles due to the fact it compensated for a control or idle problem.   It's trying to raise the idle to the correct RPM, and is doing so.   But the computer sees the high IAC count and then tries go back to the correct count, which is close to 10 or 15 fully warmed up in neutral with accessories off.   When it tries to go back to it's programming, it idles rough or stalls.

So there is something causing the car to idle too low.  If someone changed the throttle plate positions this could cause the problem.  The plate postition is set by plugging the IAC port, and adjust the plates to a specficied RPM, usually around 450 rpm, but check the specs to be sure.

Both of the plates MUST be set equally.  This is done by connect a vacuum gauge that measures in inches of water, not mercury, to the ports on the top of the TBI units, and creating an equal reading on both units, while reaching the minimum air rate ( minimum idle speed with IAC plugged).   You can use a manometer connected between the two, and balance the manometer fluid level.  This is a critical adjustment on Crossfire cars.  If the adjusting screw is still under a seal, they should be about right, barring wear at the throttle shaft.  If the seals are removed, this must be checked.  Many unknowing folks have screwed this up royally.  If this is the problem with your car, the minimum air is too low, and the throttle plates closed too much based on the reading you have of 51.

You can use the vacuum gauge, compare side to side vacuum, and adjust the throttle plates to achieve the 10 to 12 IAC counts on the fully warm, in neutral, acc off, engine.

But before you do ANY of this, make sure all other conditions are correct.  Throttle plate adjustment is the last step.

Anything that can make any car idle slow still applies.  Timing, spark plug misfire, fuel pressure or injectors, etc will all cause the IAC count to go up as the computer is compensating for the problem and trying to achieve the correct idle speed.  An EGR leaking exhaust into the intake when it should be closed can also be a cause.

A bad IAC motor will do this to you as well.  The computer command one thing, but the IAC does not respond correctly.  This a very common problem.   The count on a scan tool is only what the computer commanded, not necessarly what it did.  The only measure of what it did is the actual idle speed.

If the IAC has been removed, or the battery disconnected the computer will not properly command and control the IAC.   The IAC and the IAC count are not calibrated.  This creates computer confusion and can cause the engine to race, stall, or surge at idle.  All that is required to cause a relearn is to drive the car over 40 mph with light throttle application for a few seconds with a warm engine.  It will go through a relearn, and operate okay, if everything else is operating properly.  Again a sticky/failing IAC motor will prevent a proper relearn and prevent proper idle control.

   the scanner said that they should be set at 51 as close as we could come is 52 count. the throttle adjustment screws
are visible we have not touched them .the shop that did the
work said they were correct all they did was take my money
i found a guy that had used ones said they were good no shaft wear. gave them to the shop to put on they also put on intake gasket ( iac ) motors are new ,wires ,plugs. timing
was off reset timing when called shop to ask about timing
they said it was because of the cam but car is running better after we reset it.Ken were do we find out about what the count should be on or does the computor do that.
        mark 82

The computer does it.  There is no spec per say.  However, using a Tech I factory scan tool and performing a IAC relearn/calibration, the count comes out at or near 12.  This is per the scan tool and the GM service manuals.  My personal experience agrees.  Hence the 10 to 15 I metioned. 

The scanner 51 you were looking at is a calculated number that the computer is using trying to correct for problems.  It' shooting for it as an adjustment.  It is NOT the correct setting.  It is a failure mode setting.

The fact the screws are exposed shows that someone was screwing around with them.  I'm willing to bet they are not balanced, as well as set wrong.  Follow the procedure I metioned before, and it will help a lot.  But again make sure everything else is correct before making the adjustments.  It sounds like you have done this already.  I have straightened out many of these that someone "set" when they did not really know what they were doing.

I wish you were a lot closer.  I can do all of this in about 10 minutes once the car is warmed up, and I have the equipment in my hand.  Try to explain this to the guy with the scanner.  Perhaps have him call me in the afternoons when I am out of class.  I'll send you my number at my office at the college.

All this stuff is why I love my 78 engine with no COMPUTER Ron 7838645.6802662037

KEN
Thanks a lot car in 90% better i think the last 10% might be the cam.
            mark82

That's great Mark. Glad to hear that the CE  is running better.

 Ken is the master at the "nightmare" problems. You got to hate it when someone has had their hands under the hood that shouldn't be there in the first place. Creates to much grief for one. To bad it wasn't a simple fix from the beginning.

So why do you think that the (cam) is the 10% left of the remaining issue? Too radical to be computer friendly? Just curious.

Sarge

SARGE
Not knowing what cam is in car is my guess at the 10%.
     now that we have the car running so good the cam is more noticeable now. have a car show this weekend then none
for about three weeks so car is going back to the upholstery
shop for new door panels. then interior is done thanks for all the help and input .
               
MARK 82

Sure glad my 82 is stock and runs great.  Took off the converter a while back and that fouled the 02 sensor and the cruise would not engage.  Next I put a new stock exhaust system and all is good again.  Had the idle problem mentioned above and changed the temperature sensor in the front of the engine and that fixed it.

First year of the computer and one of two years with the crossfire equals continued maintenance learning experiences.