Surging idle. Help!

[Last5.0Cobra]

Hello all. Thank you in advance for all of your help.

My car usually idles at 1000 rpm. Right now it is surging between 900-1100 consistently. Also any sudden stops, whether i push the clutch in or brake hard... it dies.

Anyway, i looked through a lot of old posts trying to figure out what the problem is. A few days ago i cleaned the iac, and it didn't seem to help. Maybe i need a new iac? One thing that i have noticed, is if i turn on or off the A/C the problem temporarily goes away.

I actually had a similar problem to this about a year and a half ago. That one turned out to be a bad MAF. This one is different though, because its not throwing any codes.

Some other advice that i already checked was... double checking the idle screw, I have a BBK 70 mm throttle body, so the idle screw is a little allen. (the other screw is frozen) I also tried resetting the codes (even though there was none.)

I know this could be a vacuum leak, but i am not sure where all the vacuum lines are, there aren't many.... right? Anyway, sorry for the long post, and thanks again guys.

 

[hollywoodstang]

I am having a same problem here. But mine is due to deleting the EGR and EGR tube...my car dies often and can't figure out why... I set the idle little higher 800-900 and it seems to be holding.

Did you delete your EGR as well? Without tune?

Peps will help out i hope

Thanks
L

 

[Dizzy_ax]

Same thing happend to mine, while coming to a stop it starts to die down then surge back up and holds, after 10-30 seconds (while at a stop light) it will almost die and come back again. I have had two tunes with my car so far and i think the tunner forgot to tune the EGR both times. And its a pain in the ass to even get back there to have him "tune" the egr out of the system.


Some day soon i hope to get back to him and have it "tuned out" i will post in here if it actually did anything because i have tried everything...

 

[94cobra#519]

i have the same problem mainly when the engine is still cold. anyone have any ideas?

 

[sublimobile]

Ladies and Gentlemen, Boys and Girls. Gather round, cus I think I know whats wrong with your car.

Let me run down my symptoms first, as I had the same issue.

-94 Mustang Cobra - 95K miles
-when coming to a stop, idle would drop too low and then surge back up too high.
-problem was more persistent when cold outside
-coming to quicker stops usually stalled out completely
-sometimes, just stopping at a stop sign would stall the engine

So my engine was leaking oil. Thought it was oil pan and this is a job if you dont know--have to jack up the engine, so I took it to the mechanic. He said it was leaking out the valve covers---wierd? He did a little investigating and found that my PCV valve was clogged. just full of c.rap.

Anyways, I wasnt expecting it, but by replaceing the clogged PCV valve, it fixed my idle surge/stalling issue. What a nice, easy surprise.

Try it out. Its cheap and its worked for me and one other guy I told already.

Good Luck


PS: I also did the IAC reaplcement and cleaned my MAF sensor before I found out the real culprit.

 

[Last5.0Cobra]

Okay, so no i haven't deleted my EGR literally or via tune.

Funny that you mention the PCV, because i thought that it might be the culprit and purchased one from a Ford dealership last week. When i got home i realized it wasn't where i thought it was..... where is the PCV valve located on our cars?

 

[302GTS]

The PCV is in between a lower intake a hard place. It's behind the intake, I believe closer to the passenger side, but I could be wrong. I'm sure someone has a better idea, and I know I've seen a picture of where it's located, which I'll try and find tonight to post.

 

[HISSIN50]

Jeff is correct.

Replace the grommet and get a new screen (called a breather at parts stores) or clean your old one.
Use Motorcraft for the valve and grommet (aftermarket stuff doesn't fit tight enough all that often).