maybe a new idle problem.......HELP!

[mitsubluetalon]

hello all, well i've put my car back together from replacing a head with some bent valves, but now it smokes a lot of blue smoke (probably because its a used head) and it idles bad. meaning that it doesn't sound quite healthy, like the timing being way off. its not steady, like at about 900 rpm, it sounds shaky, but its not a constant skaky, almost smooth for a second then back to shaky. i've played around with the timing and the idle screw but it didn't help.

but theres another thing. when i manually rev the enging, it revs to 2000 rpm and then starts bucking between 1000 and 2000 rpm. it won't go over 2000 rpm, even at WOT. and when i first open the throttle, it almost stalls, then it goes to 2000 rpm and starts bucking.

way before i bent the valves, it did have a funny idle for a while. sometimes at an idle, it would slowly rev itself up to about 2000 rpm, and then fall to 1000 rpm and do it again. sometimes it would oscillate quickly, and eventually it stopped doing it for a while. i'm not sure if this is related but i'm pretty sure it has something to do with the throttle body

i've tested the throttle position sensor with the volt meter and i get the proper amount of resistance while moving the butterfly valve and the idle position switch is good.

i'm going to be taking the throttle body back off tonight and taking it apart. but does anybody have a clue what i should be looking for?

I'm so close to having it on the road again!! PLEASE HELP THIS POOR DSM!!

 

[Trite]

I have a 1.8, so my advice will have to be translated. But it should give you a general idea of the 2k limit problem.

Awhile back my car started doing that. It would limit at 2,000, and there was nothing you could do to get it to go past that.

For the 1.8, you can simply unplug the ISC sensor to find the source of the problem. Unpluging that sensor allows it to freely rev again. So I went ahead and replaced that sensor and haven't had it happen since.


I'm no 63 expert, but I am sure that you don't have this sensor. But I know you have an ISC motor, so you might try unplugging it or any connectors nearby when the problem occurs. If you unplug something and the car crosses 2k, problem located.

Hope this helps you somehow.

 

[mitsubluetalon]

thank you, it does..and it gives me something to think about...but i am open to anybody else's ideas or thoughts........... i appreciatte them all greatly..

an update though, i just pulled off my throttle body, and i didn't see visually anything wrong with it........i tested the TPS and the resistance ohms are in spec..i have yet to check the idle control motor, but i have a feeling its in spec.

the only other thing that comes to mind is that i just replaced my ECU while my car was down, and the ecu is from a 90 DSM, i've been told that changing pins 14 and 6 will allow this ecu to work on a 92 such as mine. i did so, and 2 mins after initial startup, the CEL came on and gave 2 codes, one for idle position switch and the other for the barometric pressure sensor, now i looked up what the pins i switched were for and wouldn't you know, that those codes were for the IPS and the pressure sensor.

i switched them back and the car started fine and no CEL. so thats good but it won't rev past 2000 before bucking.

I'm sorry to add to the confusion, but there was one other thing. when i first start up, it revs to about 1500 naturally, but when i give it throttle it goes easily past 2000 rpm until it gets warm and then it just starts bucking. so i'm mostly thinking throttle body and something to do with the coolant.

anythoughts????????????

thank you.

Jason.

 

[Trite]

Yes. That is the exact problem I had. It makes it a real bi*** to drive doesn't it?


Start the car and let it warm up. Once it starts limiting at 2 grand, go under the hood and pull the connector off of the idle position switch. Wait a few seconds and give the throttle a twist. If it goes up just fine, then you can be pretty much sure that you have a bad idle position switch.

Basically what is happening is that the switch is constantly telling the car that it is at idle, even though it isn't. Ask anyone with a idle surge and most of them will say that it surges up to around 2k then drops. I belive there is a built in idle limiter at about 2k. So when the car is constanly being told that it is idling, it constantly limits at 2 grand.

Hope this helps ya some.

 

[mitsubluetalon]

it does..........but i've tested the position switch, its only a sensor for ground, much like a hood pin switch for an alarm, i tested it through my voltmeter and its okay. i think i'm more leaning towards idle control motor, or the ecu. it is also running really really rich, and the engine sounds bad. i have no idea.