Honda Surging Idle Problems-Help Please!

[bryceban]

Howdy all,

I am having some issues with my car and I'm hoping to get some ideas on where to start. I've done some searching and talking to people over the last month but have not found much useful info. The car in question is my daily driver and I could not make my living with out it...

2002 Honda Civic LX 1.7L SOHC 5 speed manual trans with 207,000 miles.

This problem started about 2 months ago and I finally have a little time from work, family, etc. to address the issue.

The problem........

Driving around town (less than 50mph) when I shift car to Neutral and am coasting up to a stop light the engine will idle around 1,200-1,400 RPM. But, once I come to a complete stop and THEN let off of break it will come down to around 700 RPM and fluctuate from there to about 1,100 RPM.

Now exiting off of highway from 70mph and shifting to neutral while I coast to a stop it will fluctuate from 1,000 to 2,000 RPM until I come to complete stop and let off of break pedal. If I don't let off of break pedal it will continue to fluctuate. Almost as if it is related to speed, break pedal, and trans input. Which is why I'm puzzled as to where to start. I don't really have the coin right now to just start throwing parts at it or take to a shop. Any suggestions and/or help would be greatly appreciated. Thanks!

Also, when it first started doing this I had a CE light come on. I reset computer via battery disconnect and it stayed off a day or two then came back on. Then it went off on it's own and has not come back on since....

ETA: I have done the cooling system burp/air bleed and it did not affect anything. Nor has any work been done to engine cooling system prior to problems.

 

[JOD]

That sounds really familiar to a common issue with my Freestyle.

Start by thoroughly cleaning the throttle body. The throttle plate is probably hanging up on some carbon deposits and sending some wonky voltage readings to the TPS.

Next step is to test the throttle position sensor. You can easily find the test protocol online, and back-probe it, testing it with a multimeter. The nice thing (unlike my car): the TPS isn't integrated into the throttle body. So at worst, you're out $50.00 bucks.

So, I'd clean the TB first (unhooking the battery), and do it thoroughly, removing it from the car. Then, if that doesn't fix it, investigate the TPS. That should take care of it.

 

[229]

Remove intake and clean EGR ports.

 

[Lead Shoes]

Clean your idle air control valve, your throttle body and egr ports, then check for vacuum leaks.

I am assuming your problem is the idle air control valve, by the story it seems to do what mine used to do, take it off and clean it with carb cleaner.

 

[tpattgeek]

I had a similar issue, but my idle CONSTANTLY went up, down, up, down, etc. as long as there was no pressure on the accelerator pedal. It would go 800 - 2k, sometimes 3k. It was a 95 prelude and was the FITV (Fast Idle Thermo Valve). I had to replace it since it was literally broken when I took it off for some reason. Not sure if your model Civic has one, but its' worth looking into. IIRC, it was relatively cheap and easy to replace. Too bad I went months without caring to look into it. I was young...

Now that I'm thinking about it, sometimes it would just idle high (1-1.5k) when cruising in N, but just as I stopped, it would bounce up to 2k and back. Got horrible gas mileage. LOL

 

[Mr Nice]

Check PCV valve and IACV

 

[ltslimjim]

Everything others mentioned and possibly check for air in the cooling system. TPS usually don't go bad on a manual Civic. It's usually air in cooling system, IACV(aka EACV), throttle body, or EGR. Possibly a combination of them all. Vacuum hose check is worth looking into.

 

[antonmnster]

Scan the CEL. It's trying to tell you something!

 

[The_Eric]

Originally Posted By: antonmnster
Scan the CEL. It's trying to tell you something!


What he said...

 

[spackard]

If it really correlates with your brake pedal then it is probably a leaking brake vacuum booster. Inside is a rubber diaphragm. You push, it has a tear in it, lets air pass, the extra air makes it to the throttle body.

 

[ltslimjim]

^How in the world did I miss the CEL bit before?

Yes, that is the MIT right now. Brake booster vacuum line having a leak is possible.

 

[bryceban]

Thank you all for the responses. Why I love this site for everything car!

Forgot to mention that I did do the propane and hose method to check for vacuum leaks to no avail. Should rule out a vacuum leak.

I am going to pull air cleaner off and check throttle body for deposits, etc. I never considered a brake booster vacuum leak but I will check it out as it is easy enough, Thanks! The last thing I will look into is tearing off the TB and testing/cleaning IAC valve. Definitely need to check PCV/EGR valves again. Thanks for reminding.

1 question.....if the CEL has went off on it's own is the code still present in ECU? I assumed it was not therefore I did not bother with getting it scanned. If so I will start there first.

Thanks again!

 

[ltslimjim]

^The ECU probably still has it stored as a 'recent' code, worth finding out what that code is any way.