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rpmdiag, Tech and Instructor
Category: Ford
Satisfied Customers: 7612
Experience:  Since 1975
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94 Ford Explorer very rough idle on cold start. Ambiant air

Customer Question

94 Ford Explorer very rough idle on cold start. Ambiant air is about 70 in the morning. Previously, this was vacuum leak where hose popped off. Not this time.
JA: Is the rough idle intermittent or consistent?
Customer: Everyday.
JA: Are you fixing your Explorer yourself? What have you tried so far?
Customer: Tried the looking for vacuum breaks which has been problem in the past. All sensors were replaced a year or so ago.
JA: Anything else you want the mechanic to know before I connect you?
Customer: nope
Submitted: 9 months ago.
Category: Ford
Expert:  rpmdiag replied 9 months ago.

Hi, I'm Ron and I will be helping you today.
Stand by for a moment while I prepare your answer.

Expert:  rpmdiag replied 9 months ago.

The most common repair is replacing the engine coolant temp sensor.

This acts like a choke did with carbureted cars years ago.

It richens the fuel mixture for better cold start operations.

thanks, Ron

Expert:  rpmdiag replied 9 months ago.

Here's what a bad one looks like testing with a scope.

Thanks again and please remember to rate me 5 stars and keep this link in case you need me again later on.


Expert:  rpmdiag replied 9 months ago.

Hi, I'm just following up with you to see if you have any more questions.
Thanks, Ron

Customer: replied 9 months ago.

no change when I changed the CTS. I really didn't think this was the problem because it isn't what you might call "cold". It idles roughly with a loping type idle that sometimes shuts off. The hard line vacuum lines have been patched but these look sound.

Expert:  rpmdiag replied 9 months ago.

You need to smoke the intake then, it sounds like there's a vacuum leak down there.

Thanks again,