Idle goes up and down and up and down and up and down

[stangn99]

I'm having some idle issues on my 2003 2.3L

If its been sitting outside in the cold, and I start it up in the morning, it will start, rpms will shoot up to normal range when cold, and than putter and die. It doesn't always do this.

It does however ALWAYS do this. While driving and coming to a complete stop its all good. But while at the light with car in "D" and my foot on the break, I can feel and hear the car trying to move forward (reving up) and than dropping back down (reving down).

Its pretty shakey at idle, but doesn't feel like a misfire.

I've cleaned the EGR and IAC, and ran seafoam from the gas tank (which surprisingly helped with acceleration and fuel economy).


The spark plugs are new and have been gapped and checked.

Truck has 61,000 miles on it.

Could a Mass Air Flow be causing this?

[lilsport07]

is the CEL on??? another culprit could be the TPS not sending the proper signal.

[Rentz]

Check your IAC... Mine had no gasket on it, so it was sucking in air around there and making it surge. Put on a gasket and no problems.... It might also be that the IAC is bad....

[stangn99]

There is no CEL.
I also ran my code reader which apparently scans codes that do not set off CEL, and nothing came up.

I cleaned out the IAC, but realize that cleaning is not replacing.

Wouldn't the IAC make the idle stay high though? On my 99 mustang, between shifts, the idle would either stick at the same RPM I let off at to change gears, or it should shoot up really high. Never ended up replacing it as cleaning it seemed to work for the two years before I sold it.

Is the TPS something the dealer needs to replace? or is it a cheap part I can purchase and replace myself? I may do the IAC while i'm at it.

Thanks

[lilsport07]

The TPS can be gotten at the parts store. Also the IAC could be bad and causing some problems. Have you checked for any vacuum leaks?? Another thing to try would be disconnect the negative terminal of the battery to reset the computer. There just might be a override going on and it needs to be reset. The TPS can be a bit spendy i know on my 2.3L lima it was $32 and it was just two philips head screws that held it to the throttle body. But try to rule anything else out as well. I had a vacuum leak that caused it. then about 2 weeks later my O2 sensors were shot (probably were from the get go but they decided to start causing trouble at this point) then my TPS went out. Once i got all of this sorted out i still have the fault sometimes but only when my A/C is hooked up. (when its unhooked it cant cycle) But these are also tricks for the Lima engine. The 2.3L duratech is a bit different. But start out with what we were discussing about a possible vacuum leak and then the IAC and TPS and have them checked before you start spending money blindly.

[stangn99]

The TPS can be gotten at the parts store. Also the IAC could be bad and causing some problems. Have you checked for any vacuum leaks?? Another thing to try would be disconnect the negative terminal of the battery to reset the computer. There just might be a override going on and it needs to be reset. The TPS can be a bit spendy i know on my 2.3L lima it was $32 and it was just two philips head screws that held it to the throttle body. But try to rule anything else out as well. I had a vacuum leak that caused it. then about 2 weeks later my O2 sensors were shot (probably were from the get go but they decided to start causing trouble at this point) then my TPS went out. Once i got all of this sorted out i still have the fault sometimes but only when my A/C is hooked up. (when its unhooked it cant cycle) But these are also tricks for the Lima engine. The 2.3L duratech is a bit different. But start out with what we were discussing about a possible vacuum leak and then the IAC and TPS and have them checked before you start spending money blindly.

Thanks for all the info.
I will look into the TPS and IAC.

I guess i'll start with checking for a vacuume leak, since it doesn't cost anything. I've always hated trying to find a vacuum leak. I tried finding one on my civic once, and just made a mess! I had TB Cleaner ALL over the wires and everything, and never did end up finding the leak.

Is there a more efficient way to find a leak? or should I stick to spraying throttle body cleaner all over the place?

thanks again.

[lilsport07]

starting fluid works better for me.

[stangn99]

I haven't gotten around to getting the IAC or TPS.

However, I'm starting to suspect there is a leaky injector.

When it sits overnight, and I start it up it shakes and RPMs drop struggle and engine eventually dies.

At the same time there is quite a bit of (i think) white smoke, and it absolutely stinks like gasoline.

After the second try, the motor will run and everything smooths out.

[rshrimp]

Thanks for all the info.
I will look into the TPS and IAC.

I guess i'll start with checking for a vacuume leak, since it doesn't cost anything. I've always hated trying to find a vacuum leak. I tried finding one on my civic once, and just made a mess! I had TB Cleaner ALL over the wires and everything, and never did end up finding the leak.

Is there a more efficient way to find a leak? or should I stick to spraying throttle body cleaner all over the place?

thanks again.

I use an acytlene torch unlit to search for a vacume leak.
Just open the actylene valve and use just like carb cleaner or ether.
Works the same and no mess!!!!
A propane torch unlit would work the same

[lilsport07]

I use an acytlene torch unlit to search for a vacume leak.
Just open the actylene valve and use just like carb cleaner or ether.
Works the same and no mess!!!!
A propane torch unlit would work the same

That is a good idea. never thought about it. But that will work great.

[W04RFR]

How do you do this vacuum leak checking? While the engine is running spray it around the hoses?

[Ponyguy]

How do you do this vacuum leak checking? While the engine is running spray it around the hoses?

Yes, that's the way it's done. I'd be leery of using acetylene or propane around a running engine, because you can't see where or how much you've sprayed the stuff.

You spray a little mist of starting ether around the suspected leaky hose connection or suspected gasket leak, and listen for an increase in idle speed. Where you shoot some stuff and the engine speeds up, you've found the vacuum leak.

[W04RFR]

If I use starting fluid will this damage my engine if it is a turbo?

[Ponyguy]

If I use starting fluid will this damage my engine if it is a turbo?

No.