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I think you might have a couple problems happening at the same time here, but this is where I would start: Most of the symptoms you describe can be caused by a gummed-up control pressure regulator, particularly during the warm-up time.  The screen on the inlet side commonly gets clogged up on cars that have been sitting a long time without being driven.  It is an easy part to swap out with a known good one for testing, but remember that its function relies upon the engine heat generated from the valve cover.
You will also want to check the mixture adjustment as it can cause some stumbles and hesitation as well.
Another item that every owner should check is the full-throttle microswitch.  I've seen a lot of these failing lately, and they usually fail in the WOT position, making your mixture way too rich and wasting a lot of gas.  If it is working, you should feel a distinct click when you press the switch and your idle should stumble a bit.  Then (most importantly), it should return to normal when you release it.  The easiest fix for that switch is just to disconnect it, but if you like things to work the way they are supposed to (like me), replacement is easy and relatively cheap.
Jake Kamphoefner

----- Original Message ----
From: mike clemens <rmclemns@xxxxxxxxx>
To: dmcnews@xxxxxxxxxxxxxxx
Sent: Sunday, July 6, 2008 5:08:04 PM

Josh's car has once again got me stumped. Here's what is happening: Start the car up and it idles right on specs, try to give it gas and it wants to hesitate and almost quit. Back off the gas, it goes back to idle. As the car warms up, you can get more and more rpm but never full throttle. After the car is warmed up to where the fans come on, the idle hunts up and down, between 650 and 850 rpm. The car starts backfiring if you try to go above 5000 rpm. If you move the throttle off the microswitch that controls the frequency valve, idle stabilizes at 950-100 rpm.

The plugs are new, the idle speed motor is new, the injectors have been cleaned by JH and are all working. All vacuum lines have either been checked or are new, no leaks.

Any ideas of what might be wrong?

Mike TPS 1630


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