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Steve, Auto Service Technician
Category: Car
Satisfied Customers: 5494
Experience:  25+ yrs experience as a professional working technician; ASE L1 master technician
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1990 s10: whit my idle up and down and jerks whats wrong

Resolved Question:

I have a 1990 s10 pickup 4.3 engine, when it in drive whit my foot on the brake it idle up and down and jerks whats wrong.
Submitted: 10 years ago.
Category: Car
Expert:  Steve replied 10 years ago.


The symptoms you describe are consistent with a vacuum leak. On the 4.3 vortec engine that you have in your truck, the usual source of the problem is an internal vacuum leak caused by the EGR valve not closing completely. If you have a scan tool available, take a look at the EGR position reading; it should be at zero when the truck is idling.

If you do not have access to a scan tool, take the EGR valve off of the engine and look at the bottom: you will probably find a small chunk of carbon holding the pintle partially open.

I hopoe this is helpful; if so, an accept would be most appreciated! Thanks!

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