I have a 98 F150 5.4. Very rough idle when engine warms up. RPMs also drop. Sometimes the engine will just shut off. This was a progressive problem. At first the check engine light didn’t come on but now it has. When I accelerate the problem goes away and the truck runs fine. If anything it might feel like the truck is being held back a little. Gas consumption has increased also. Any ideas on what the problem might be or how to troubleshoot?

 

Welcome to the site!

Go to AutoZone, Advance, etc. and get them to read the code. Do not buy anything from them (yet), come back hear and post the code that was read, and do a search on the site for similar posts. Sounds like your Idle Air Control needs cleaning or replacing, but that usually doesn't throw a code. You may have a mis-fire, but the codes should reveal what's going on.

Good Luck!

Jamie D.

 

T55, go back out to the engines forum and read my thread about "Rough Idle"....read thru it

 

Clean the throttle body, the tuck ran a lot better, but it didn’t fix the problem. Found the problem to be the line that runs from the PCV valve and connects just below the throttle body. The rubber elbow had a hole in it. FYI, Ford doesn’t sell just the elbow, they make you buy the whole line, $52.00.

 

$52 seems kinda steep for a hose. I replaced the one on my 99 Expedition when I changed plugs and it was only $20. It came with the PCV valve and I thought that was a bit steep. I was told those hoses usually get soft and collapse, making it hard to diagnose.

 

I agree, $52 is very steep. I told the dealer I only needed the rubber elbow at the end of the line and he said it only comes as an assembly. He also said there are 2 different types of lines that come off the PCV valve. One has a V split in it, which was mine, the other doesn’t. That may have added to the cost of mine. I don’t know if that was a dealer only part. I didn’t shop around to see if anyone else had one. Maybe I should have, just didn’t have the time.