So I have this idle problem.

If the car is cold, then starting it, it wont run below 2000rpm until it hits moderate operating temperatures, and you have to hold the gas on to do this. You can make it run below 2000rpm, but you have to feather the gas. When its warm, it runs and all, but when you start off, you have to have it up around 3000-3500 and get up to a decent speed before fully depressing the clutch, otherize it will be a very jerky and powerless start.
Now stopping/slowing down, when the car is cold, as soon as you let off the gas it dies, not sure if its normal but im used to it on my trans am anyway. When its warm, if you press the clutch in and apply brakes, and let it idle while stopping, the rpm drops and runs 100-300 bouncing and fluctuating, and attempts to die the entire time. Sometimes if I sit at a light without the brakes on, just sitting, It will idle slightly higher but still fluctuate.

Heres what I did prior to this happening. I found a couple wire caps the previous owner had put under the hood and traced them to fix, I found one is to the sensor on the exhaust exit pipe (dont know the technical name?) of the turbo, sticking out the side, guessing its a fuel/air ratio sensor, it T's off into a guage on the dash, and to another wire that comes out of the main harness above the water pump. This wire is shielded on the inside, so im guessing its a positive with a braided negative on the outside.
I DO NOT KNOW WHAT THIS DOES <-- sadface
So I left that disconnected in fear of shorting something out until I find more, in which I cannot find more, so I will take a picture in the daylight.

I also took out the fuel pump in hopes of fixing the fuel level sending unit, which appeared to be fine, I found a twisted together wire on the fuel pump harness and butt connected it so it had a proper connection, maybe this isnt right or didn't get a good connection, but I'm running out of wire length coming out of that harness. I looked up the wire and its the blue white stripe wire, which is supposedly the sending unit wire only, so it shouldn't matter.

But knowing this is a turbo car, and I have heard vacuum caps come off quite frequently on them, I thought I would check that, but I cannot find all the vacuum ports, and it sounds like a vacuum problem to me anyway.

I got this car last Thursday and it ran like a top, perfect, idled at 750-800 with no problem at all, all the time. So between then and now something changed.

 

I have a 90 Convertible with a Tii swap and I have the same problem. When cold it "shunts", but once warms up it is fine. I am not very mechanically inclined, but my mechanic spent hours trying to get rid of it an wasn't able to. He said it may be due to the larger porting on my car, or maybe a slight air leak in the intake manifold.
I am planning on replacing soon, I will let you know if it helps. Good luck in the mean time.

 

Hey mate,

From what you've described the sensor on the exit pipe is the O2 sensor. It's job is to read the exhaust gas coming out and modify the fuel mixture accordingly if it's too lean/too rich, if it fails you'll be running full rich all the time or have all sorts of problems, if it's disconnected, reconnect it! Your ECU doesn't like not getting a reading from the O2 sensor and will do all sorts of crazy stuff to try and get a reading from it.

My car bounces and fluctuates between 1200-1500RPM and it drives me nuts, still haven't worked out the issue. Sounds in your case like a bad vacuum leak or a misadjusted TPS perhaps? Get a copy of the service manual and go through that vacuum diagram make sure everything is connected, then test/adjust the TPS as well. Also check your BAC hasn't become disconnected somehow, as this controls idle and all sorts of crazy stuff can happen if it fails.

 

Whel, the car doesn't have emissions, and the BAC is disconnected, was when I got it. The wire that goes to the O2 sensor is disconnected, but I don't know how to reconnect it as its like a 2-pole wire, ground on the outside, and the positive wrapped in its own insulation on the inside. But I don't know how they go. Since its a turbo conversion though, don't I wanna run at least a little on the rich side, which means it should be disconnected anyway?

 

Well get a bac on your engine! I don't see why people take those off...

My car doesn't have jumping idle, I don't have the stock o2 connected anymore. You sure you don't have any intake leaks?