Howdy all. The saga continues....

My 99 Civic EX 5 speed (121K miles) idles like crap once warmed up. It idles around 650 rpm when warmed up which is about 100 rpm too low, and as a result the car shakes like a couple of rocks in a Maxwell House coffee can. I step on the gas and bring rpm up to around 750-800 or so (indicated) and it immediately smoothes out. Bottom line is idle rpm when warm is too damn low.

I've replaced the Idle Air Control valve, the spark plug wires and the two main ground wires, all with Honda OEM parts. New NGK plugs, both regular and platinum. All grounds cleaned down to bare metal. Timing checks perfect at 12 degrees IAW shop manual. Increasing idle speed through idle speed screw does nothing except trigger 'check engine' light (and subsequent reversion into 'limp home mode' where car runs like crap). Idle speed screw is currently set by dealer at upper limit of travel. I've had it in to dealer and he's been putting computer monitor on it and can't find anything wrong; he's scratching his head.

Slightly stepping on gas pedal at traffic lights to keep rpm up around 800 or so fixes problem. I'm thinking of fooling the system and simply adjusting the throttle cable to it gives a slight tug on the system. Hell, aircraft control cables stretch and need periodic replacement.

Any other thoughts or suggestions??

 

Alot of forums post this issue with the Civics and fixes range from the obscure coolant level to ECU reset. Some even go as far as TPS, doubt that one , or PCV replacement. Also some point at Vacuum leaks. If you get this one fixed post a reply as I'd love to know what fixed yours.

 

OK, gang. Read all the stuff that I did to my car in the above thread first so you have a background regarding all the stuff that's been done to fight this problem.

Next: My dealer mechanic (notice I said dealer. Problem like this is one for a dealer, even though you pay through the schnozz, in my never to be humble opinion.) contacted his Double Secret Probation Honda Tech Line that only Honda Dealer mechanics have access to. They told him to check the motor mounts, as they can and will transmit vibration through the frame.

Sure enough, today they found two of the four motor mounts were Kevlar/Urethane and were shot to s**t. Why the hell the original owner would replace only two mounts, and then replace those mounts with Kevlar/Urethane mounts is beyond the scope of my comprehension. The dealer mechanic replaced the effected motor mounts. The other two rubber OEM mounts were in great shape so they left them on the car. They also did this thing called "indexing the motor mounts" where you literally lift the engine off the mounts and then let the engine down again on the existing motor mounts. (In my case they did this on the two original mounts and the two new rubber OEM motor mounts.) This has the effect of literally 'reseating' the engine on the mounts.

Well, I'll be durned, but replacing those damn Kevlar mounts with OEM rubber mounts and re-indexing all four mounts did the trick. This car idles like a sewing machine now. Those Kevlar mounts had wear marks on them that you could literally feel and see. The lead mechanic re-checked the idle specs with the computer and it was dead-on perfect. You simply wouldn't believe the smoothness now.

So after changing the entire planet out (and spending copious amounts of money in the process) the problem is solved. The good news is that I now have brand new spark plug wires, grounds, a brand new IACV, new platinum NGK plugs, and the new motor mounts. This should do me for a while!

I really hope this helps some other poor shmoe out there with idle woes. The mechanic told me that the Honda mechanic help line advised him that Civics are really prone to warm idle problems so perhaps my experience will help someone else.

Mike

 

Huh, never would have fathomed that. My guess was vaccuum leak...My Si is having a much much milder, but similar problem. Mine is prolly a tiny vaccuum leak, I hope!