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?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  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: What else can be done

You should have an engine compression test done to see if one or more cylinders are low on compression. If the spark plug insert is not installed correctly or leaking compression it will be identified in this test. If the...

Q: Transfer case leak

Hi. The transfer case leak is a very common issue with these vehicles, especially at high mileage. The problem occurs when the pump for the transfer case begins rubbing against the side of the case. Over time, it will drill...

Q: Transmission quits working completely until I turn it off, then restart it, and then it works briefly, quits again.

if the engine speed is increasing and the vehicle does not move, the transmission is slipping. The first thing to do would be to let the engine idle and warm up to operating temperature and then check the transmission fluid...

Related articles

How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.