Mechanics

CLOSED LOOP IDLE PROBLEMS

Chevrolet Truck

1993 Chevy 1/2 ton, 5.7 L, 4 WD, 5spd, 167,000 miles:

Once the truck reaches operating temperature it can't maintain an idle and dies. At steady highway speeds, there is a sudden loss of power.

Two different shops have not been able to correct the problem. I was told there were no vacuum leaks on top. They said the engine was in good shape. One shop adjusted the new IAC valve I had installed. The shops said all sensors appear to be properly connected and functioning. A new mass airflow sensor didn't change condition. The intake manifold gaskets were replaced and timing reset. In between shop visits I replaced the stock computer box with a remanufactured unit with no change in problem. Since coming back from the shop, the service engine soon light has NOT come on despite the problems.

Note: The vehicle previously had a Vortech supercharger installed. All supercharger components have been removed and returned back to stock form with the exception of the additional inline fuel pump. I had earlier replaced the stock TBI with a rebuild ported Turbo City version. I also have tri-y headers (with O2 sensor), replacement cat, and low restriction exhaust currently installed.
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Jrwerner
August 23, 2007.




Does the check engine light come on when key is in on position?You said the MAF was replaced? 93's were TBI and dont have MAF's, wondering what was replaced, maybe the MAP sensor. Has there ever been any codes in the ECM? When it is idling, what does it do? Surge? Miss? Also just to be sure, what is the 8th digit on the vin#? K?
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Tiny
Jack42
Aug 24, 2007.
Thanks.

No check engine light comes on. Code 15 is in memory. I believe the code relates to the coolant sensor. (When I unplug the coolant sensor the truck runs better but triggers a check engine light.) Correction, the shop tried swapping the MAP sensor for a new one but said there was no change. The truck starts and idles fine for roughly 10 minutes until it reaches a normal operating temperature at which point the idle fluctuates a number of times from about normal idle speed to about nothing. Pressing on the accelerator keeps the motor from dieing. The first shop recommended the new intake manifold gaskets and new computer. After I fixed both, and brought to the second shop, they recommended a new computer (which was already replaced). K is the letter in the 8th digit.

Tiny
Jrwerner
Aug 24, 2007.
When it had the supercharger on it they probably installed a coolant sensor that tells the PCM that it is colder than it is to make it richer. Try a new A/C Delco coolant sensor.

Tiny
Jack42
Aug 26, 2007.

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