I've been fighting an idle problem ever since I got my truck (93 150 300 I6 5 spd 4x4 3.55 grs). My mechanic told me it was probably the Egr valve and that I could just block it off with some gasket material, so I did, any way that didn't work, it ended up being the throttle body needed cleaning. Anyway it gets horrible fuel mileage, around 11 or 12 (on the hwy). I've got to get it to get better mileage, it's been on the computer, it doesn't pull any codes (except for the egr, but since it's blocked off I don't worry about that one). I put new plugs, wires, cap, rotor,fuel filter,air filter, and a battery.. oh yeah when I put the battery in the next tank of gas I ran I got like 16 mpg, then back to 12, that makes me think it should do better, I just can't pinpoint what the deal is......I know this is alot of crap to digest, but any help would be appreciated..

 

Wow I used to get 23mpg with mine. I did have my EGR go bad one time and I lost 1MGP till I got it fixed. 12MPG should be way off the norm. Sorry I cant help you just wanted to give you the info on how my MPG went with a bad EGR.

 

I've had it almost a year, and it's never gotten good gas mileage, except when I put the new battery in...

 

Possibly a bad o2 sensor?

 

Or a bad ECT (engine coolant temperature) sensor. Either can deteriorate and cause the engine to run rich without throwing a code

 

I know where the o2 sensor is, but where is that ect sensor located and about how much does one cost, I'll replace both of them If I can get better gas mileage...... thanks

also, what are some symptoms when the ect starts to malfunction, my truck during the summer dies right after startup, only when it hasn't been driven for awhile, if it's warmed up it does fine. ( my mechanic told me that the throttle body was probably dirty and that's what was causing it to die). hasn't done it once since it got cold though

 

dirty throttle body? ive never heard of that . you could try cleaning your IAC valve, mine had some surging problems at startup (sometimes it would die right when you start it) and cleaning the IAC took are of it.

 

Goofy question here...whats the IAC valve?

Like you Donate54, every once in a while my truck will run rough for a second then die right after it starts. When I start it up again, it runs fine. Like I said, it doesn't do this very often.

 

IAC - idle air control valve (i think, someone correct me if im wrong). do you have a haynes or chilton manual or something similar? theose will help you locate it, but its prettu much attached to the side of the throttle body.

 

Ah.....ok, I know what yer talking about now. Thanks.