Idle issue

Asked by May 16, 2017 at 07:22 PM about the 1994 GMC Sierra 1500 K1500 SLE 4WD Standard Cab LB

Question type: Maintenance & Repair

When at a stop truck goes from 2500 rpm to
500 rpm back and forth. Smooths out in
neutral. Runs great on the go. New
distributor, egr valve and sylanoid. Fuel
pump and filter 18 months ago. TB looks to
be fogging fine.

6 Answers

1,575

IAC valve or did you do that already? There is a vacuum leak somewhere. Good Luck!

1 people found this helpful.
Best Answer Mark helpful

That is next. I'm also pretty sure a vacuum leak as well. Thank you.

Damn. New IAC but same issue. No more check engine light. Shifts smooth. Mechanic said he believes performance chip bad. Discontinued. Dealer wants 450 for new ecm (I think that's right).

1,575

I have one more idea that is concerning a vacuum leak possibly with the brake booster that I thought should be checked since you mentioned when you brake at a stop this issue happens. There is usually a check valve before the brake booster...it might be bad or the vacuum brake booster might have a pin hole in diaphragm. Thought I'd throw that in there before you shell out $ on the ECM. Also if it is the ECM is it possible to open the unit up? If it's just a bad solder joint you might be in luck and be able to DIY the thing. If not perhaps you can find a used one. Good Luck!

Makes sense. Breaks are always going soft. Adjusted rear drum, new fro

Any way to diagnose. 300$

Your Answer:

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 56,460 nationwide Sierra 1500 listings starting at $1,500.

ZIP:

GMC Sierra 1500 Experts

  • #1
    dragonflyoffshore
    Reputation
    5,640
  • #2
    John Saffrahn
    Reputation
    4,030
  • #3
    Glenn Clingenpeel
    Reputation
    3,800
View All

Related Models For Sale

Used Ford F-150
2,266 Great Deals out of 187,689 listings starting at $495
Used Dodge Ram 1500
328 Great Deals out of 8,863 listings starting at $2,495
Used Toyota Tacoma
459 Great Deals out of 50,124 listings starting at $2,850
Used Chevrolet Tahoe
646 Great Deals out of 37,769 listings starting at $1,995
Used GMC Yukon
326 Great Deals out of 23,849 listings starting at $2,000
Used Chevrolet Camaro
306 Great Deals out of 26,931 listings starting at $2,500
Used Jeep Grand Cherokee
1,148 Great Deals out of 80,317 listings starting at $1,500

Used Cars For Sale

2019 GMC Sierra 1500 For Sale
18 listings starting at $33,000
2018 GMC Sierra 1500 For Sale
33 Great Deals out of 30,679 listings starting at $21,760
2017 GMC Sierra 1500 For Sale
99 Great Deals out of 5,272 listings starting at $16,983
2016 GMC Sierra 1500 For Sale
48 Great Deals out of 2,889 listings starting at $15,990
2015 GMC Sierra 1500 For Sale
73 Great Deals out of 4,875 listings starting at $11,995

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.