Rough Idle

BigCope923 · Aug 18, 2017

A few days ago I pull up to the gas pump and my truck stalls out. Never did that before and I didn't think too much of it. Filled up on regular unleaded fuel at Sam's. I put in 10 gallons to top it off.

The truck sputtered once or twice on my way to my next stop. I'm thinking that maybe the gas was bad. So when I'm done at my next stop I go to start the truck and it won't start. The engine turns and turns, but never catches. So I get it towed home.

My mechanic comes by and checks it out. He gets it to start, but it continues to idle up and down. He takes it and proceeds to try and diagnose to no avail. He reports that the truck will start, but continues to idle up and down. And while driving it runs like it's not getting enough gas. For instance, if you press the gas pedal to the floor, it barely goes.

Looking to see if anyone else has experienced this issue before and what a possible diagnosis could be. Thanks in advance for your help!

BIG_KID · Aug 18, 2017

Id start with a fuel filter then move to a plugged converter

ram1220 · Aug 19, 2017

Any engine or other warning lights on the dash lit? I had this issue twice on my 90 Sierra 5.7. The first time it was a clogged fuel filter. The other time I had a bad distributor cap. The truck would fall flat on it's face when pressing the accelerator. No check engine lights on these occasions. I did have a third time where the truck would constantly idle up/down but it never stalled. I had a check engine light only at highway speeds after about 5 mins of driving. I changed the O2 sensor and EGR valve and problem solved. Just some ideas to look at.

BigCope923 · Aug 21, 2017

ram1220 said:
Any engine or other warning lights on the dash lit? I had this issue twice on my 90 Sierra 5.7. The first time it was a clogged fuel filter. The other time I had a bad distributor cap. The truck would fall flat on it's face when pressing the accelerator. No check engine lights on these occasions. I did have a third time where the truck would constantly idle up/down but it never stalled. I had a check engine light only at highway speeds after about 5 mins of driving. I changed the O2 sensor and EGR valve and problem solved. Just some ideas to look at.

Yep, the service engine light was on. My mechanic pulled a code today that came up as "Electronic Timing". Are you familiar with that?

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ram1220 · Aug 22, 2017

No sorry I'm not.

rydeon · Aug 25, 2017

Going through the same issue. My truck pulled code 43. Which is basically knock sensor. But. I have a suspicion that its knocking due to lean condition due to fuel pump. I tested knock sensor, replaced map sensor and tested tps. rebuilt my tbi with new diaphragm for regulator and truck runs like crap. I ordered a new Delphi fuel pump and strainer just to know that it will be new. I have no idea how many miles on used up old truck i bought. You can rent fuel pressure testers for tbi from auto stores if your pump is new and dont suspect that is the problem. 13psi??? i think. Still working to figure it out with alot of help from great people on this site. Let me know and i will post my findings when my fuel pump and strainer arrives.

rydeon · Sep 2, 2017

BigCope923 what code number was pulled for your truck?? If your fuel pump is newer or has been changed please test pressure because its not alot of fun to change fuel pump. Mine has arrived and waiting for a second set of hands to replace. The idle up and down on your post is exactly what mine started doing. If you get it figured before me let me know. I am changing my pump anyway just because i have no idea how many miles are on it. Will post when i rip it apart.

DerekTheGreat · Sep 5, 2017

If you got code 43 try and disconnect that tan wire with the black line on it from behind the cover inbetween the A/C drier and passenger side valve cover. It'll be taped up if it's never been messed with before. If it runs just fine without that connected then the ignition module/dizzy is no good. The dizzy in our '89 K1500 was completely trashed. I changed the cap and rotor which killed it in the driveway, wouldn't idle but would run if I pressed the gas some. Ran just fine with that wire unplugged. New dizzy and it's been going fine ever since. Well, as good as an engine with a burnt valve will run anyway..

Rough Idle

BigCope923

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BIG_KID

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ram1220

I'm Awesome

BigCope923

Newbie

ram1220

I'm Awesome

rydeon

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rydeon

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DerekTheGreat

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