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Car idle loops high rpms to low rpms
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ryanhornor
Novice
Oct 4, 2009, 2:42 PM
Post #1 of 10
(2574 views)
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Car idle loops high rpms to low rpms
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1990
Honda
Prelude Si/abr
2.0l B20A5
151k-200k miles (odometer was tampered with around 2003, im guessing 20k to 50k are missing)
I am considering buying this car from a local dealer. The car seems mechanically sound and the engine looks good (nothing too visibly worn). However, when I turn the key it will idle fine until I rev up the engine. When I let off the gas and let it return to idle, the engine then starts cycling from about 900 rpms up to 1800 rpms in 2-3 second intervals. It will continue to do this until the engine is shut off.
The dealer told me that the problem just began a few days ago and that it is most likely a clogged or damaged pcv valve (which costs only about $5 to replace). Is it possible they are keeping something from me? Could it be a larger problem? The car is beautiful for a 19yo Honda, but I cant afford to have the engine rebuilt right after I buy it. Thanks for the help!
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Hammer Time
Ultimate Carjunky
/ Moderator
Oct 4, 2009, 3:35 PM
Post #2 of 10
(2567 views)
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Re: Car idle loops high rpms to low rpms
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Yes, it is likely much more serious than that. There are 2 things I have seen act that way on a Honda and they are the IAC (idle air control) which can be worth over $300 without labor. The other is a decel valve that some of them have that can be just as expensive. If he thinks it's so simple, tell him to fix it first.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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ryanhornor
Novice
Oct 4, 2009, 4:14 PM
Post #3 of 10
(2562 views)
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Re: Car idle loops high rpms to low rpms
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I am pretty sure it is the pcv valve that is causing the problem, cause if you remove it and shake the valve loose the problem stops for a while. This indicates to me that it is the valve getting gunked up and sticking that is causing the problem. I am more concerned as to what is causing the valve to seal shut. I read online somewhere that when an engine is dying, the pressure sometimes gets too high in the chambers and forces excessive amounts of oil into the pcv valve causing it to gunk up and stick way earlier than it should. Any thoughts?
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Hammer Time
Ultimate Carjunky
/ Moderator
Oct 4, 2009, 4:17 PM
Post #4 of 10
(2558 views)
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Re: Car idle loops high rpms to low rpms
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Great, go buy the car.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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ryanhornor
Novice
Oct 4, 2009, 4:39 PM
Post #5 of 10
(2554 views)
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Re: Car idle loops high rpms to low rpms
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Ummmm....was that sarcasm?
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Sidom
Veteran
/ Moderator
Oct 4, 2009, 4:51 PM
Post #6 of 10
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Re: Car idle loops high rpms to low rpms
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I doubt the pcv valve is causing the problem. With Hondas they run coolant thru the IAC and they get gummed up & cause this exact problem and they are expensive.
If you think it's the PCV, those are very cheap & easy to change. Get on & put it on and take if for a drive......
Catch anything HT?
(This post was edited by Sidom on Oct 4, 2009, 4:51 PM)
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ryanhornor
Novice
Oct 4, 2009, 4:59 PM
Post #7 of 10
(2541 views)
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Re: Car idle loops high rpms to low rpms
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Thanks for the reply Sidom.
I think this car is a bad idea, I'd hate to buy a 19 year old lemon.
I do have one last question though: Is it true that pcv valves going bad and gumming up really quick is a sign of excessive pressure in the engine?
If so, will replacing the pcv and taking it for a test drive be enough to indicate whether this is a routine wear and tear issue with the pcv or a problem with a bad engine generating excessive pressure?
Hope this makes sense, thanks again for the help guys.
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Sidom
Veteran
/ Moderator
Oct 4, 2009, 5:07 PM
Post #9 of 10
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Re: Car idle loops high rpms to low rpms
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Yes if the rings are worn, then you will get excessive blow by which will clog things up faster.
Honestly if it was just pcv valve, don't you think the dealer would put this few dollar part on so they wouldn't have to try to explain this surge as "maybe something minor"
Hondas are good cars but with a 20 year old 200k car expect problems.
(This post was edited by Sidom on Oct 4, 2009, 5:08 PM)
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