2003 2.3L Frustrating High Idle

[Henk]

Hello all.

I recently bought my first vehicle, a 2003 Mazda B2300. When I first bought the vehicle, the idle was a little high, around 1100 - 1200 RPM.

However, soon (1.5 hours after I bought it) it developed into a real issue; the truck ran at 3500 RPM on start-up, accompanied with lots of white smoke and the Check Engine Light came on. The truck continued to run at 3500 until I put it into gear and started to move, but it would still pull (albeit now running at a lower RPM) with my foot off the accelerator pedal. Disconnecting the IAC immediately brought the truck to a stall.

I brought the truck to a friend, who ran the code, which pointed to the IAC. I played with the throttle butterfly valve so that it's open a fraction. Now I have a very low idle with the IAC unplugged, and it's liable to stall until it's warmed up, but at least it'll run.

The airbox was on improperly, so I reseated the filter and closed the airbox correctly. I tried pulling the IAC and cleaning it with electrical contact cleaner. I disconnected the negative battery terminal for around 30 minutes while I cleaned the IAC. I also cleaned the electrical contacts for the TPS, IAC, and MAF sensor and put on a dab of dielectric grease to try and rule out poor connection issues. This had no effect on the high idle. I did not clean the MAF sensor, although I noted it looked very clean.

I tried pulling a similar IAC from a 4.0L Ranger. It had the same harness connector and bolt pattern. I left the one-piece blue gasket in the manifold in place, and on start-up the vehicle ran properly still idling a little high, but very manageable at perhaps 1100 RPM. I paid for the part ($10) and went back to the truck. On start-up however, the truck once again jumped to 3500 RPM and lots of white smoke.

After unplugging the 4.0L IAC, the truck continued to run at 3500 RPM. Returning to the original IAC the truck wanted to run at 3500 RPM. It was only after reinstalling the old IAC and unplugging it that the truck would finally drop down to a barely stalling idle.

So now I turn to The Ranger Station for anyone with some advice or insight with this issue.

 

[adsm08]

Well, we have a few problems here. You used contact cleaner to clean the IAC, that stuff is not nearly strong enough. Carb cleaner is more appropriate.

Next, you messed with the throttle adjustment. Even if you get a good IAC on it, it may not idle properly now.

Have you tried spraying around the intake with carb cleaner or brake cleaner? It might help show a vac leak.

 

[marauderx]

What he said^^^ also, are your power brakes holding vacuum when you shut it off? Brake boosters do fail...

 

[Henk]

So I replicated yesterday's issue today. I returned the throttle to normal, took off the original IAC, installed the none I pulled from the parts yard. I disconnected the battery while I worked. When everything was buttoned up, she started sweet, idling at 900 just like it should. I took it out for a short drive and bought some gas, tidied up, etc, but when I went to start it again, she idled a little higher, perhaps 1200 RPM. A couple hours later when I started it to see if things had changed, I was looking at about 2500 RPM, although it seemed to search around a little. Finally I started up again (this was perhaps 4 or 5 starts since "fixing" the problem) and she jumped right up to 3500 again, lots of white smoke.

I've seen lots of people point to a vacuum leak as the issue; could a vaccum leak still manifest itself with these symptoms?