4 cyl. shaky idle

harleyboy07 · #1 11-25-2009, 01:24 PM

have 99 4 cyl. FI. when trk. start,all is ok. When it starts to idle down. It almost cuts off, idles up,slows daown and shakes, for about 2-3 mins. then levels out. seems to run ok. But idles down very low and almost cuts off. This up and down has no rhyme or reason. Other than at statrup. Have replaced idler air control on back of throttle body. And fuel pressure regulator valve in tank. Any ideas before I start replacing parts. 196,780 mi.

zbinck2.3 · #2 11-25-2009, 06:35 PM

i doubt its anything with the fuel. Which means air or ignition, i would just replace the plugs plug wires. Is there a check engine light ? for almost 200000 miles the possibilities are kinda endless.

scooby stew · #3 11-26-2009, 02:24 PM

welcome from the uk

DangerRanger01 · #4 11-26-2009, 02:37 PM

My 2.5l does the same thing. At idle it'll dip up and down to were its almost dieing. I guess its normal, lol. I'm at 51,000miles so...idk. Someone told me it was because i use synthetic oil, but i have no idea the truth behind that.

Fx4wannabe01 · #5 11-26-2009, 04:00 PM

Disconnect the a/c compressor electrical plug. Could be totally possible that the load it puts on your engine when it cycles, causes enough of an rpm drop to cause it to almost die. If disconnecting it helps out a ton, I suggest putting in an in-line switch to interrupt the battery power to the compressor.

As said above, any check engine lights? How's the maintainence on the truck? At 200k, problems could be practically endless.

FoMoCo · #6 11-26-2009, 11:35 PM

my 2001 2.5L did the same thing, now my 06 2.3L doesn't do it

twinjetguy · #7 11-30-2009, 07:38 PM

I recently replaced my coil packs with Accell coil packs and cleaned the mass air flow sensor. I was amazed with how much smoother the truck ran. Might want to check those out as well. Summit Racing sells the coil packs for around $69 each pack. Don't need to get both, just get one for the intake side. Just make sure to use electrical parts cleaner on the mass air flow sensor also.

bnuts5150 · #8 03-21-2010, 11:43 PM

My father in law uses carb cleaner on the intake is there anything wrong with that???

Scott · #9 03-24-2010, 02:47 PM

I'm guessing here, but it sounds like you have a leaky gasket somewhere in the intake. The way you describe it sounds to me like a cold gasket leaking air until the block warms up, which warms the gasket up, expanding the gasket and therefore eliminating the leak/surging. I replaced the cylinder head in my 2.3 awhile back and had this problem. I over-torqued the lower intake manifold gasket and cracked it. Mine was pretty bad though, it would surge constantly. I finally took the intake off and it was pretty obvious that I had created a HUGE vacuum leak. New gasket - CAREFULLY torqued (23-25 ft/lbs i think) - and it runs like new now. I'd use some high temp silicone on the new gaskets too. Good luck.