High Idle Problems

[kdowney50]

I have a '94 B2300 2.3L 4Cyl with 164K miles and a manual trans. The engine idles at 1200-1500 RPM all the time. I can some times get the idle down to 700 RPM if I drag the clutch while holding the brake. However, this does not always work. Any ideas what could be causing this?

[Mirage]

My first thought is to check the IAC (Idle Air Control) solenoid. I found my truck doing the exact same thing one morning. Drove it that way for about a week before taking everyone's advice and pulling the darn thing to look at it. Sure enough, the valve was stuck due to carbon build up. Cleaned with Throttle Body safe cleaner, exercised a few times, and been working like a champ ever since.

[kossdust]

Yeah check IAC same with mine.

[kdowney50]

Hey gang, Remember me? I had an ongoing problem with high idle on my '94 Mazda B2300. I replaced the IAC, and most of the vacuum hoses trying to solve this problem. Nothing worked.

However . . .I MAY have found a solution.

I was hooking up my boat trailer yesterday and could NOT get the light to work. They worked last week so I was really scratching my head over this one.

I spent most of the afternoon troubleshooting (when I would rather be sailing!) and eliminated EVERYTHING from the trailer lights forward. Finally, I removed the solid-state device that changes a five wire light system to a four wire system and hooked the lights to the truck's electrical system directly.

During the drive to the marina I noticed my high idle problem was gone! Again this morning on the way to work it was still gone. Now I HATE problems that fix themselves. But it makes me wonder: Could a faulty electrical device waaaaay back under the rear bumper cause a problem with the IAC waaaaay up under the hood? They are both electrical devices. As far as I know, the only thing those two devices have in common is the chassis ground. I am half tempted to dig that thing out of the trash and reconnect it to see if the problem returns.

Stay tuned. This is getting exciting!

[MountainMike]

I am gonna stay tuned, my Ranger does the same thing. Bookmarked

[big b]

or try tps mine did that i put new iac on and the tps was of bad ohm reading put new one on its gone now

[kdowney50]

The water pump gave out last week. When I pulled it off I found the impeller was all but gone! Replacing the pump solved two problems: The cabin heater had quit working (separate post) and I had this idle problem I couldn't track down since last spring.

Your probably wondering what the water pump has to do the idle. Me too!.

Consider: idle is determined by a lot of different things, including engine temperature. All these sensors (02, throttle position, water temperature, fuel pressure etc,) are sending information to the Powertrain Control Module. The PCM uses this info to set the idle. If the water pump is not circulating hot water past the thermostat in the heater hose, then the PCM is getting bogus information on actual engine temp. Thus the PCM sends an "idle up" signal to the throttle position solenoid in order to increase the RPM's until the engine warms up to operating temperature.

What clued me in to this was the heater hoses going into the firewall. They were warm near the water pump but cold near the firewall. This led me to speculate that there was a lack of water flow past the thermostat. This lack of flow caused a false temperature reading to the PCM. This false reading led the PMC to think the engine was below normal operating temperature. Therefore, the PCM was trying to keep the engine at high idle until it warmed up.

Until some automotive engineer tells me I'm full of it, that's my story and I'm sticking to it!

Hope this helps.

[dangerrangerstx]

throttle position sensore or take ur tooth brush and carb cleaner and clean ur butterfly in your throttle bodie

[dangerrangerstx]

it can be your throttle position sensor or take ur tooth brush and carb cleaner and clean ur butterfly in your throttle body

[kdowney50]

Originally Posted by dangerrangerstx

it can be your throttle position sensor or take ur tooth brush and carb cleaner and clean ur butterfly in your throttle body

Sorry, didn't mean to confuse anyone. I looked over my last post and see where I could have been more clear. I've made some changes. Hope it helps. It seemed clear to me only because I have been knee deep in the problem for the last year. Let me know what doesn't make sense to you and I will try to make it plain.

[sittenHIGHon35s]

so tell me this did your truck read like it was always running cool except when u drove it for a long while before u changed the water pump cause mine does the same high idle i replaced the iac valve the high idle went away but recently came back after a few months and this mornin the gauge started reading hot after a short drive with it being in the 40 degree. range out side and it always has taken a long time to heat up even in the Florida sun in the summer now u got me wondein if the heating and cooling of my truck and my high idle have sumtin to do with each other u got me scratchin my head man and if maybe my gauge has been wrong all along

[kdowney50]

Yes, that's what I'm saying. Get your engine up to temp and feel the heater hoses from the engine to the firewall. If one is hot and one is cold, you probably have a water pump problem. If your engine takes a long time to warm up, you most likely have a thermostat problem. (Probably stuck open) If you now have overheating problems, it could be the thermostat stuck shut or a bad water pump. Either way, buy a new thermostat, water pump, antifreeze and flushing kit. Flush your system thoroughly (don't forget to flush the heater core) and replace the pump and thermostat.

Once that is done, let us know what effect it had on high idle.

Best of luck.

[BONES]

Cool, another helpful thread!!

I'm out to clean my IAC and check out the TPS. Maybe my TB is all gunked up too, will check it all out, this damn idle problem is getting rediculous.

Can these problems make yours hard to start when the engine has sat all night, gets a hard start?

[kdowney50]

I was begining to think mine was the only one with this problem. Looks like its more common than I last thought. Between us, we're bound to find something that works. Hey bones, Whats a 'TB'?

[BONES]

Well someone had posted above that the Throttle Body (TB) butterfly could be gunked up and stick open a bit, so I'll check that too. The part on the engine with the throttle cable hooked to it.