New PCM needed for my '98 Civic's idle problem?

January 7, 2007 1:19 AM

So I had a '98 Civic recently serviced after sitting for 6 years. The idle is intermittently shifting between roughly 1000 and 2000 rpms every 15-5 seconds depening on how warm it is.

Now they say I need a PCM - $750 new, or a cheaper aftermarket or some such. I won't know if it's given a scanner code until Monday. I'm thinking about asking them to double (or just check) _all_ the sensors attached to it and double check the vacuum systems on hunches from what I've seen on forums. For the record I've no idea. First I hear is that it was misfiring when they first started it and a suspect fuel injector was eliminated and/or fixed. Although I have very good faith in the shop I've taken it to, I just want what's best for the car and my wallet.

Good news is the tires seem OK so far and the brakes are solid and checked out as having little wear but are slightly squeeky. I've only driven it about 40 miles though.

What are some popular forums some of your better informed gear heads visit, please?

Or... Had any experience w/98' Honda Civics w/idle problems. The car has 34K miles and has been sitting in a carport for six years.

posted by prodevel to Shopping (17 answers total)

I had an '87 Civic that did the same thing. Fortunately, my cousin was also my Honda mechanic. He said that was a common trait among Hondas, and not to worry about it or spend any money fixing it. I eventually came to look at it as the car telling me when it was done warming up.

That said, the engine on a '98 model might bear little or no resemblance to the '87 model, so take it with a grain of salt.
posted by nadise at 2:41 AM on January 7, 2007

Not Honda-specific, but I'd be suspecting other things before the PCM - crook air flow metering (AFM or MAP sensor) for one; gummed-up/perished injectors for another; maybe even a poisoned / dying O2 sensor. Hell, all the sensors - cold start / temp, knock, etc, etc.

I'd wait until they check the diagnostic code - and then, if they still told me it was the PCM, I'd take it somewhere else to have the diagnostics run again.

But, if you feel confident they've done the obvious things like that (and changed the fuel / flushed the fuel system) then yeah, it might be the PCM. Definitely wouldn't be at the top of my list, though.

And I wouldn't be trusting 6 year old tyres for too long either if it's been sitting on them...
posted by Pinback at 2:46 AM on January 7, 2007

I had a '93 Civic that displayed the same symptoms. It ended up being the water pump.
Word of advice: most reputable shops will replace the water pump on Hondas when they replace the timing belt. This is good, because the redundant labor involved is tedious and expensive.
Whenever you have the timing belt replaced, make sure they replace the water pump too.
posted by ktrey at 8:13 AM on January 7, 2007

It could be the PCM but there are much cheaper things to check first.

It's something affecting the IAC motor, so it could be a bad IAC motor, a bad temp sensor, any where in between or a bad ECM.

If it works fine once it's warmed up, my suspicion would fall on the IAC or temp sensor.

IANAM.
posted by Tacos Are Pretty Great at 9:38 AM on January 7, 2007

Honda-tech.com is pretty much the de-facto forum site for Hondas on the internet. Yes there are a lot of annoying riceboy kids on there, but almost no question asked, with the right information, will go unanswered. I'd explain your problem there in the Civic forums and see what comes up.
posted by autojack at 10:12 AM on January 7, 2007

I've found lots of good advice at the forums at Super Honda.

This is probably not your problem, but just in case... I had my Honda ('96 accord) display the exact same behavior immediately after the radiator was replaced. From the list of possible causes in this thread, it turned out to be air bubbles in the coolant. I topped it off, ran it, topped it off again, ran it until it stopped.
posted by everybody polka at 11:02 AM on January 7, 2007

my first thought it is that it sounds like a slight vaccuum leak....... check all rubber hoses for signs of cracking and dry-rotting..... (not the radiator hoses)

second thought would be the temp sensor.....

pcms usually will not go bad just from sitting....... unless it was exposed to alot of moisture.....
posted by peewinkle at 2:23 PM on January 7, 2007

Does it have A/C and is it working ? It's possible that the A/C has lost its charge but is still attempting to cycle, and the ECM is attempting to compensate for what it thinks the change in idle load would be if the A/C was working. Just a guess, as I have never worked on a Honda - but the change in cycle time based on how warm it is made me think of air conditioning.

Also, some cars have an A/C pressure sensor that the ECM reads - maybe this is bad.
posted by rfs at 7:22 PM on January 7, 2007

Also, ECMs and PCMs have very high NTF (no trouble found rates) - they are frequently blamed for intermittent wiring and sensor problems which can be hard to diagnose.
posted by rfs at 7:25 PM on January 7, 2007

If the extent of the issue here is a flaky idle and you're not seeing poor gas mileage, loss of power when you're actually at load, or poor emissions quality then I'd ask... why would you spend $750?

Aside from that, I'd also be real skeptical if a mechanic jumped to a $800 repair without giving me a serious list of the other cheaper possible solutions they'd tried or ruled out first. Maybe you need a second opinion.
posted by phearlez at 7:31 PM on January 7, 2007

Check Car-part.com for cheaper (used) parts. A used ECU, for example, is about $100.
posted by LordSludge at 9:05 AM on January 8, 2007

Response by poster: To update: I drove it a bit more and with the a/c and radio on it triggered the check engine light. I took it in and I'll ask what the scan and current 'autopsy' is.
posted by prodevel at 12:09 AM on January 10, 2007

Response by poster: argh forgot to mention that it was accelerating mildly while driving after I got asked to drive it mildly. The check engine light went on shortly after I turned the a/c and radio on.
posted by prodevel at 12:14 AM on January 10, 2007

Response by poster: also it idled correctly after warming.
posted by prodevel at 12:24 AM on January 10, 2007

Instructions on checking the thrown code yourself.
posted by phearlez at 9:49 AM on January 10, 2007

Response by poster: OK so here's what happened.

I was told to drive it a bit to 'shake something loose' for about 100 or so miles. It happened to take quite a bit less. After driving for a while, it happened to be a fairly warm day so I turned the A/C on while also having the radio on. The check engine light came on pretty quickly. After the light came on it seemed to surge slightly at times as if it was doing the same thing it did while idling. But the idle problem went away after this kicked in - strange.

I took it back and they immediately cleaned the throttle body as I'm told. The car is now running perfectly.

Thanks very much, all.
posted by prodevel at 10:55 AM on January 13, 2007

See my answer here.
posted by mlis at 9:56 PM on February 4, 2007