Rough idle 99 gmc k1500 5.7

Asked by Oct 24, 2016 at 12:03 PM about the 1999 GMC Sierra

Question type: Maintenance & Repair

Truck idles very rough but once it's over 30 mph it
seems to drive just fine until stopping or slowing
below 30mph. I have replaces plugs twice, wires,
fuel oump, fuel filter, relay fuse, full distributor. Any
ideas?

1 Answer

310

Could be a vacuum leak , but I suspect it's the MFI . (Multiparty fuel injection). This is a notoriously plagued system .I had it on my suburban as has just about anyone with the same.set up . It's called the (Spider injection ) .and it's a faulty design from day one .they make upgrades that will alleviate all of the problens associated with then. Rough idle , bad throttle response ,missong/skipping port all around performance. Now I'd check for a vacuum leak and make sure you've gapped spark plugs correctly etc. Just to be sure all other avenues are explored before looking into replacing and upgrading the MFI . It's about 100 bucks more than going back with the original set up ..it's a world.of difference aND brings new life to your engine .Good luck

Your Answer

Add photo

Related Questions

Search GMC Sierra Questions

GMC Sierra Experts

#1 Js08016
Js08016
Reputation 110
#1 dandyoun
dandyoun
Reputation 110
#3 John Saffrahn
John Saffrahn
Reputation 80
View All

Related Models For Sale

Used GMC Sierra 1500
774 Great Deals out of 68,507 listings starting at $1,800
Used Chevrolet Silverado 1500
1,914 Great Deals out of 182,757 listings starting at $1,495
Used Ford F-150
2,126 Great Deals out of 193,350 listings starting at $290
Used Dodge Ram 1500
403 Great Deals out of 10,927 listings starting at $1,000
Used Chevrolet Camaro
351 Great Deals out of 31,326 listings starting at $2,200
Used GMC Sierra 2500
166 listings starting at $3,195
Used Toyota Tundra
442 Great Deals out of 34,570 listings starting at $2,500
Used GMC Yukon
406 Great Deals out of 20,427 listings starting at $1,495
Used Cadillac Escalade
203 Great Deals out of 10,930 listings starting at $2,500
Used Chevrolet Tahoe
585 Great Deals out of 32,920 listings starting at $1,500

Used Cars For Sale

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.