Q: The truck intermittently, has a very rough idle, and runs rough,usually after warming up.

asked by on

The truck was running fine until a fill up a few weeks ago. Shortly after I filled the tank, it started running rough and idling rough. I ran some sea foam, and then fuel injector cleaner through it. Then changed the fuel filter, and now have changed the spark plugs. I had changed the plugs previously and wires at 100k. The truck seems to run fine when cold, but once at operating temperature, the idle becomes very rough, and sluggish on acceleration. I have also cleaned the M.A.F., the EGR valve, and checked the pcv valve. Motor appears to change and run better if I disconnect the MAP, but not convinced that's the issue. The fuel economy has been about 15mpg for some time, down from 19 mpg when new. Had a mechanic put on a test, and the reading was first a bad O2 reading on cylinder 4. Then, cylinders 1,3, and 5. Sometimes, the Check Engine light blinks. It did cut off (the light) at first when I changed the plugs. O2 sensors have never been changed.

My car has 172000 miles.
My car has an automatic transmission.

Hello. This can be caused by a number of different things. If this occurred right after you had gotten fuel then I would start by testing the fuel pressure. I would do this when the vehicle starts running poorly. It is possible that the bad fuel contaminated the fuel pump and it is not putting out the right pressure. If the fuel pressure is fine then I would check the other sensors readings with a scan tool. One other common thing that I have seen on this engine is a leaking intake manifold gasket. It starts leaking on the bottom side and that leak causes the MAF and MAP to not read correctly which causes it to run like this. If you would like to have this rough running condition looked at, consider having a YourMechanic certified techniciancan come to your home or office to diagnose why it is running rough.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. The truck intermittently, has a very rough idle, and runs rough,usually after warming up.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: dust problem rear hatch

Hello. Thanks for writing in about your 2011 GMC Terrain. There may be a problem with the outside dust cover not sealing properly. This could cause dust to get inside the car. If the rear hatch isn’t sealing properly, this...

Q: Cigarette lighter fuse blows while replacing it, what will cause this?

There is at least 4 different systems that this truck has for the cigarette lighter power adapters. Most of the time, it is something that is being plugged into the adapter or the adapters are shorted. You should look in...

Q: Can I repair the 5/16 nylon fuel line (high pressure line) with a splice of the smaller 3/8 nylon fuel line using a hose splice?

Hello. The fuel line is under fuel pressure and should only be repaired using a repair that is using an approved repair with certified parts. Using the wrong fuel line repair parts may cause a fuel line to rupture causing...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.