Rough Idle Issues
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Senior User
Joined: Apr 2011
Posts: 178
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From: West Allis, WI
Rough Idle Issues
I have a reoccurring issue with my truck.
Its a 92 F150 with the 351W.
Normally it idles decent with a light miss and idles smooth when a cold fresh startup but when its warm or has been idling for over 30 seconds it will start getting rough and seems like its going to stall. I've replaced the TPS and have fixed some bad vent lines but the idle is still bad. As soon as I give it some throttle it runs beautifully.
I don't even know where to start looking...
Thank you
Its a 92 F150 with the 351W.
Normally it idles decent with a light miss and idles smooth when a cold fresh startup but when its warm or has been idling for over 30 seconds it will start getting rough and seems like its going to stall. I've replaced the TPS and have fixed some bad vent lines but the idle is still bad. As soon as I give it some throttle it runs beautifully.
I don't even know where to start looking...
Thank you
Senior User
Joined: Aug 2001
Posts: 275
Likes: 1
From: Lexington Park, MD
I agree with the tune up as priority #1. I have to speak on something I just did to mine that GREATLY enhanced it's idle quality. I guess its old news, but I have to speak on it. Its the PCV vacuum hose swap. After some studying up (I just happened to stumble onto it on this site), I swapped the brake booster vacuum hose to the PCV vacuum port and the PCV vacuum hose to center intake vacuum tree (had to purchase a length of 3/8" line and some clamps). The idle immediately improved. Evidently the placement of the PCV at the back of the intake loads down the #8 piston with all those gasses and over time can cause piston failure, terrible idle etc. I was also finding oil in the air filter box so I had nothing to lose in trying it. If you dont have that problem this may not help you. I think Ford rerouted the PCV tube to the center of the intake on the 1994 or 1995 trucks, but I'm not sure. Someone will correct me. There are many old threads on this at this site so please look it up before you try it. If you have already, no loss. Definitely do a tune up though. Good luck!
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