84 Prelude idles rough

[Bobiii84]

My 84 prelude only has 92k miles but for some reason it sometimes just wants to idle poorly. It is dual carbureted, manual, has idle advance etc. but even when the engine is hot, it some times just wants to die. Any1 have any clue what my problem is. Also a honda mechanic a while back did an emissions test on it and said my carbs where in perfect condition???

[jwd3jdm]

could be a number of things. Could be your ingnition wires or your spark plugs or a huge number of things. Is your check engine light on? If so you need to get it hooked up to an engine diagnostics machine. If not then i would suggest taking it to a mechanic unless you know enough to start taking things apart and checking them.

[AcesHigh]

Okay, I guess the idle problem with Preludes is one of the more common problems. We're seeing alot of these lately. A semi-definitive answer for the FAQ:

Problem: The car has erratic RPM idling. It may even stall (die) on you when you stop putting in the gas. When parked, you may note that the idle jumps up and down. When you rev, the idle goes up, starts falling to 0RPM, and then stalls. So why?

There can be a billion things wrong with your car that can cause a jumpy idle.

First thing I'd check is the TPS (Throttle Position Sensor). Use a voltmeter to check the voltage of the sensor to make sure it's working properly. If it isn't your idle will be erratic. Use a manual to find the proper voltage... I think it is .5 volts closed and a little less than that at WOT (wide open throttle).

Now check your IAC (Idle Air Control) Valve. It's on the back of your Air Intake Manifold. Unplug it. Doing that should make your idle go up if the IAC is working as it should. If it doesn't, you've found your problem. Go to the dealer, grab a new one, install it, and go out and buy a Coke because you're done. If your idle does go up, turn the little bypass screw on the side of the throttle body and bring it down to about 500rpm. Once you plug in your IAC valve again, you should be hitting normal speeds again, 700-800rpm.

If this fix doesn't work, you've got yourself a headache ahead of you. Check everywhere (!!) for vacuum leaks. All your hoses and lines. You need to seal up the leak. Doing so should fix up your idle problem. No? Well read on.

Now is where we need to determine if your car is stock or not. Messing with fuel/air can cause rough idle. Bring back fuel pressure to stock levels (get a manual for that). Sometimes if you bore your throttle body it can cause problems. If you have a chipped ECU (or a bad one), it could also cause problems.

If you're still reading, well... take your car to the dealer or mechanic. Because I've ran out of ideas.

[88 ROCKET]

Good call by "ACE"... also check your pneumatic solenoid valves in the "black box" under the hood with all the vacuum lines running into it. I had a bad Bypass Control Vacuum Solenoid that was causing my Idle problem. Three dollars at the junk yard... $83.00 at the dealer, and they are the same valves used in damn near every honda/acura.

[crzyCollegeKid]

any ideas what could cause my car to shake momentarily when the radiator fans turn on?? i know its because the rpms drop too low in idle, but is that normal, or what?