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Pete
Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 26750
Experience:  14 years GM dealer Technician.
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GM Siverado: The last time my 99 Silverado with a 5.3 Vortec

Customer Question

The last time my 99 Silverado with a 5.3 Vortec started it was running 4000RPM, I shut it off and started it again and the same thing happened. I revved the engine up to try to get the RPM's to ideal down, it went down to 1000RPM's and right back up to 4000RPM's. I shut it off and started it again, but this time it just barely would start and I had to give it some gas to keep it running. I shut it off and tried to start it again and it wouldn't start at all.
I checked the fuel presser and found that it was bleeding off, so I changed the fuel pump. It is holding good fuel presser now and has fire but will not start. I also took the throttle-body off and cleaned it. The truck didn't show any codes and has never shown anything in the message center other than service engine soon.
Submitted: 1 year ago.
Category: Chevy
Customer: replied 1 year ago.
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Expert:  Pete replied 1 year ago.
Hi,my name is ***** ***** I will be happy to try to assist you with this.I may need more information in some cases to help with answering your question.
One common issue I have seen with the high idle is the intake gaskets on this model leak.They were a poor design and allowed air to enter the engine that wasn't being monitored.The new style gaskets are thicker and better material.GM released a bulletin to replace the intake gaskets for intake gasket leak issues.This won't show up as oil or coolant leaking but instead excess air leaks past the gaskets into the engine causing a high idle and in some cases rough running.
The other issues I have seen are a faulty throttle position sensor sending an incorrect signal causing the engine to either not start or idle high or a faulty engine computer commanding the idle to high causing this.The throttle position sensor signal can be checked with a scan tool to monitor the data signal from it to see if it is faulty needing replaced.
If you have not had the updated gaskets installed this should be done as well.The old style gaskets were orange and the updated are a teal green in color.
Thanks Pete
Customer: replied 1 year ago.
I replaced the intake gaskets a few years ago because of a issue with the engine loading up when I would first start it and go. If I would let the engine run for a little while before I put it in gear and go it would run fine. But if I started it and put it in gear to quick it would run terrible for a little while.
I just hooked a Snap-on Solus diagnostics scanner up to my truck and the TPS shows 4.03 at ideal position and 4.73 with the pedal to the floor. Can anything else effect the Volt rang of the TPS or should it always have rang from 1.50 to know more than 5.0 Volts? What else should I check with the scanner?
Expert:  Pete replied 1 year ago.
If you unplug the TPS does it show 0 volts at all.If it does and no wiring is found to be shorted or damaged at the TPS this sounds like the TPS itself at fault needing replaced.The TPS should read near .5 volt at idle and around 4.5 to 5 volts at wide open throttle.
Thanks Pete