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

GMC Sierra Experts

  • #1
    Js08016
    Reputation
    120
  • #2
    dandyoun
    Reputation
    110
  • #3
    John Saffrahn
    Reputation
    90
View All

Related Models For Sale

Used GMC Sierra 1500
1,242 Great Deals out of 71,071 listings starting at $1,750
Used Chevrolet Silverado 1500
2,693 Great Deals out of 196,286 listings starting at $699
Used Ford F-150
3,184 Great Deals out of 239,109 listings starting at $1,300
Used Toyota Tundra
684 Great Deals out of 38,182 listings starting at $2,900
Used GMC Sierra 2500
160 listings starting at $5,795
Used GMC Sierra Classic 1500
15 Great Deals out of 333 listings starting at $3,595
Used Dodge Ram 1500
412 Great Deals out of 11,096 listings starting at $1,499
Used Toyota Tacoma
732 Great Deals out of 50,704 listings starting at $1
Used Cadillac Escalade
269 Great Deals out of 12,721 listings starting at $2,000

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.