Tired Of Trouble Shooting

pennzoil29 · April 17, 2008

I'm sure this has all been discussed before, but here is what's happenining, and what I've done to try and fix this problem. This damn thing idles spuratic, aka as up and down. Sometimes revs up on its own. The tach will start to come down below 1k rpm, and then go back up to 12 sometimes 15k making it harder to brake, not alone driving me up a wall. Here is what I've done, I'v cleaned maf, replaced tps,iac,and removed throttle body and cleaned it up shiny new, yes I put in a new gasket. I still have the problem. Also a while back when it was freezing, I had to r&r my camshaft sensor, while doing so, I tried to move the main vacuum line from the brake booster out of my way and the damn fitting that goes into the intake manifold cracked. I also replaced that at a later date, and upon doing so, I found that one of the little ears on the fitting had broken off and had fallen into the engine. I did not know this at the time and have been driving with that piece of plastic inside my engine. I'm not lucky enough for it to be laying in the valley of my '99 5.7, so I'm sure it wound up in my valve train some where, possibly #4 cylinder. I can not find any vacuum leaks doing conventional methods. I replaced lower intake gasket 2 yrs ago. SORRY this is so long, but any suggestions would be taken to heart. I am also sorry if this has been discussed before. I did search, that is why I did what I've done so far. Thanks, Jeff

MustGoFaster · April 17, 2008

does it have the CPI injector system?

if so - it's possible that's the culprit. when these things go bad all kinds of stuff happens, idle screwed up, cuts out randomly, crappy gas mileage, injector leakdown, running rich, goofy hesitations that cant be tracked down to sensors - and worst of all no dang codes get tripped.

IF thats the problem - the only real remedy that I know about so far is complete replacement, but get out a jar a vaseline first.... people have fixed them, but only after lots and lots of cursing.

I think the most creative solution I've seen tho is to get a marine intake manifold and have an egr and a few other things machined into it, then you can switch to standard injectors, but IIRC you will need a new computer.

***edit - you have a 99 5.7? - I think they had a different form of FI***

id say fuel pressure regulator, and or dirty injectors next. how many miles? had a funny intermittent idle/miss condition with a jeep once that had 150+ on the clock. prev owner put thousands into fixing it and eventually gave up and put it for sale. after doing a cam sensor, crankshaft sensor and a couple of other things. had the injectors serviced - turned out that 2 of them were on the very lower limit of flow spec, and it was just enough to make the thing run funny. replaced those 2, and put in the cleaned ones - ran perfect ever since.

pennzoil29 · April 18, 2008

does it have the CPI injector system?

if so - it's possible that's the culprit. when these things go bad all kinds of stuff happens, idle screwed up, cuts out randomly, crappy gas mileage, injector leakdown, running rich, goofy hesitations that cant be tracked down to sensors - and worst of all no dang codes get tripped.

IF thats the problem - the only real remedy that I know about so far is complete replacement, but get out a jar a vaseline first.... people have fixed them, but only after lots and lots of cursing.

I think the most creative solution I've seen tho is to get a marine intake manifold and have an egr and a few other things machined into it, then you can switch to standard injectors, but IIRC you will need a new computer.

***edit - you have a 99 5.7? - I think they had a different form of FI***

id say fuel pressure regulator, and or dirty injectors next. how many miles? had a funny intermittent idle/miss condition with a jeep once that had 150+ on the clock. prev owner put thousands into fixing it and eventually gave up and put it for sale. after doing a cam sensor, crankshaft sensor and a couple of other things. had the injectors serviced - turned out that 2 of them were on the very lower limit of flow spec, and it was just enough to make the thing run funny. replaced those 2, and put in the cleaned ones - ran perfect ever since.

Thanks, buddy. I never even gave the fuel injectors a thought. I have a little over 158k on her. It has the sfi injector system. I stopped at a buddys garage, and he is going to put the scope to it tomorrow. I did notice this thing is pretty carboned up inside the intake when I had the tb off, actually pretty ugly. Thanks again.

bronyaur · April 18, 2008

Just a thought, but if you've got a bad plug wire/plug/cap/rotor etc., every time you get a miss the rpms will drop and the IAC will cycle, causing the rpms to go up.

MustGoFaster · April 18, 2008

probably right, I guess I assumed that he had already done a plug/wire change.

pennzoil29 · April 18, 2008

Just a thought, but if you've got a bad plug wire/plug/cap/rotor etc., every time you get a miss the rpms will drop and the IAC will cycle, causing the rpms to go up.

all new in February

probably right, I guess I assumed that he had already done a plug/wire change.

You assumed right. I did all of that in February if I'm not mistaken. Unless I got ahold of a bad plug or any of it was defective out of the box. I just don't know, but I hope to find out tomorrow. The damn thing is going to the garage for service. My dumb ass is to stressed out to fool with it any more. I'll let everyone know what the problem was, hopefully. Thanks all

pennzoil29 · April 19, 2008

Well, it looks like my pcm might be taking a sh*t on me. We had it hooked up to a scanner and bypassed the computer and the bitch ran fine. I played around with the tps and as far as I can tell it isn't wanting to take off on it's own. Everytime I would get going down the road , some sob would pull out in front of me and crawl. I'm getting a loner pcm on Monday, thanx to a friend that owns a junk yard. That way I'll know for sure before I go out and purchase one. I'll keep you all up to date. Thanx to those who replied.