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Working on a 90 GMC Sierra 1500 4x4 with a 5.7. When I got my hands on it the idle waved really bad after it warmed up. To the point of dying. Driving or parked it would do this. I found that the throttle body gasket had a good size piece missing. Replaced it. When I had the throttle body off it was clogged where the pcv valve comes in. Cleaned up the entire throttle body and replaced the valve. Still had the problem. Changed the map sensor. No change. Had the ignition control module checked and it checked out fine. Took the fuel filter off and was dirty. Changed it and the waving went away but have a high idle now. Checked and changed the temp sensor and tps, but still have the high idle and quick shift on the tranny. Will idle fine here and there and the service engine light goes off when it does but after a minute or two it either dies or goes back to high idle. Looking into the idle air control valve or the pcm. Any suggestions?
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If you are using the gauge that came with the vehicle it's accuracy is not great. These gauges were designed so that at a glance you can see the needle is pointing basically to the middle of the dial. As long as the needle is more od less there, you're okay but the numbers mean nothing due to the gauges in accuracy. If you really want to check the oil pressure, the procedure is pretty easy but requires decent equipment as well as the knowledge of where to tap into the pressurized oil system.
I had to replace the mass air flow sensor. $ 150. the engine would shut off when driving too.changed fuel filter only worked for a day. The sensor is just after air filter.
I own a 93 GMC and I have had this happen a few times, First its a chevy they are cold blooded take a bit to warm up and get heat. That and im sure the oil had not warmed up and gotten up to the top end. Let it warm up then try it out.
This could be a number of things but i think that your problem sounds like a vacuum leak or an EGR problem. Try listening for leaks and try un-plugging the EGR solenoid valve one time.
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