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rpmdiag, Tech and Instructor
Category: Honda
Satisfied Customers: 6721
Experience:  Since 1975
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I have a 1990 Honda Pacific Coast. It runs fine except:

Customer Question

I have a 1990 Honda Pacific Coast. It runs fine except: after about thirty minutes of driving the idle RPM goes from normal(###) ###-####to 3000 Plus. Therefore, when you release the throttle in this condition (when it has been run for over a half hour) it backfires. The local mechanic can't figure it out. Help.-Jon Reiver
Submitted: 3 months ago.
Category: Honda
Expert:  rpmdiag replied 3 months ago.

Hi, I’m Ron and I’ll be helping you today.
Before we get started though, Please understand that I don't know
your skill level or tools you have to assist us. Also understand that
I can't see, smell, hear, or touch the vehicle either, so patience is
appreciated. JA is a great Q/A site, but it does NOT replace a
repair shop.
My goal is to make you happy and get a great rating in return for
my time. Sometimes I have to give you bad news that I know you
didn’t want to hear, so please don’t shoot the messenger.

The best thing to do in a case like this is scan the computer for codes and related data. The idle air control motor on the throttle body may be the problem. You can take it off and clean the carbon out of it and also clean the throttle body to and see if that helps.

Thanks, Ron

Customer: replied 3 months ago.
Ron, it is a 1990 and I don't think it has a computer that can be scanned. I might be wrong. IT always idles correctly when cold. Any thoughts?
Expert:  rpmdiag replied 3 months ago.

Yes, it should give data with the proper tool and software. God only knows how much that costs:)

Try putting on a coolant temp sensor. These can be real brats if their out of calibration too hot or too cold reading. If you have a lab scope, that's even better than the scan tool. See attachment.

Thanks again, and please don't forget to rate me and keep this link in case you need me again later on. Ron