My 94 Metro (1.0MT) loses it's fast idle when cold - not all the time but the colder the outside temp the more frequent it becomes. You have to sit and baby it with the pedal till it warms up.
Also, I've noticed an idle surge when warm - I can actually see the ISC motor opening the throttle in conjunction with a click from the purge canister soleniod. This isn't nearly as annoying as the cold idle problem.

No codes, no vaccum leaks, engine is well tuned, everything else works fine.

SO - is the idle controlled by the ISC motor (black box bolted to the rear of the TBI body, 5 wires in harness) or by a wax pellet air valve discussed in Haynes? I would think the ISC does the job, but if there is no wax pellet why is there coolant circulation thru the TBI? I can't see the wax being intermittant, but could see the ISC doing that. If it is the ISC, has anyone ever dismantled one of these? Can they be purchased aftermarket, or only with the TBI assy?

Love the posts here - hope someone else has run across this before - Thanks!

My 94 Metro (1.0MT) loses it's fast idle when cold - not all the time but the colder the outside temp the more frequent it becomes. You have to sit and baby it with the pedal till it warms up.
Also, I've noticed an idle surge when warm - I can actually see the ISC motor opening the throttle in conjunction with a click from the purge canister soleniod. This isn't nearly as annoying as the cold idle problem.

Both of these symptoms may indicate a throttle position sensor out of adjustment. It is fastened to the TB in line with the butterfly shaft, on the opposite side of the throttle cable. It is held on by two phillips head screws with slots in the sensor to allow for adjustment. You can do it by ear or with a DVOM (digital volt/ohm meter). To do it by ear: Get the engine to operating temperature, loosen the screws (they strip easily, use the proper size screwdriver), and turn the sensor until the idle lopes up and down, then back it off til the idle smooths out. This will get you in the ball park. If you like, I'll post the 'proper' adjustment procedure via a DVOM.


SO - is the idle controlled by the ISC motor (black box bolted to the rear of the TBI body, 5 wires in harness) or by a wax pellet air valve discussed in Haynes? I would think the ISC does the job, but if there is no wax pellet why is there coolant circulation thru the TBI? I can't see the wax being intermittant, but could see the ISC doing that. If it is the ISC, has anyone ever dismantled one of these? Can they be purchased aftermarket, or only with the TBI assy?

I don't believe these cars have a wax pellet to control idle speed. At least I haven't seen one in the 93-2000 model year fleet I keep in repair. So far as I know the PCM controls idle via the ISC, ignition timing and injector pwm. Coolant runs through the throttle body in order to prevent the butterfly valve from sticking in cold weather.

-MechanicMatt

Thanks for your assistance MM. I've adjusted the TPS and smoothed out the idle, I'll give it a few days to see if the cold idle works now - it's been like that since I bought the car 3 years ago. Funny how the little things are the most annoying... :)

Well even though the idle irregularity has been smoothed out, I still have no fast idle 8 times out of 10 when the engine is cold. I assume the temp sensor is OK because there are no codes. I know the ISC motor works when warm from the previous surging problem.

Has anyone ever had an ISC stick? Has anyone ever disassembled the ISC, or is that a no-no?

The car runs great the rest of the time - once I warm it up for 2 or 3 minutes we're good to go :)

Yea, I would kind of like to know more about this "fast idle" too. Mine never has idled up on a cold start. I may pull the TB down later towards spring, to check a couple more things, but some tips would be appreciated.

The cold start fast idle system is built into the back side of the TB. There is a wax matrix pellet inside the TB that expands and contracts with the coolant temps. When cold,the matrix contracts, opening a valve that allows more air to enter the TB ( thru that hole on the backside of the carb) and increase the idle. As the coolant warms, the matix expands, closing the valve and cutting off the additional air supply. This system tends to weaken as our cars age. You can not replase the wax pellit thing. But you can remove the valve and spring and clean them from all the carbon that builds up on them.

Seach this forum. DoctorBill has some great photos of what this system looks like. You have to remove the TB to get at it. You can not replace the wax pellit thing, but you can clean the valve and spring inside. You have to turn the valve to unscew it from the TB. Count the number of turns to unscew it. Then when you put it back in add one turn. By adding 1 turn you are in affect opening the valve a little more allowing more air to enter the TB.

Make sure that when the car warms up, it comes off the fast idle. If it doesn't you have to unscew the valve 1/4 to 1/2 turn to get the valve to close when hot.

The FSM has a procudre to adjust the valve by putting the TB in hot water until if closes. I found my way above a little easier to do. Idid this on my 91 and it solved all of my "no fast idle on cold start" prolblems.

BUT before you do any of this, change the coolant temp sensor on the back of the TB, its cheap and just because you don't have a code doesn't mean its not working 100%. Make sure that the coolant holes that lead to the senosr in the TB are free of rust. They can clog and prevent coolant from getting to the senosor, thus flase coolant sensor readings to the ECM.

I have many of these sensors and can send one to you for shipping charges only, but I need a pic of yours, there are two differnt types of wire harness connections to them.

I will see if I can't find those pics of the open TB so you can see what the heck I am talking about.

OK here is the link to doctorbill's picks:

http://www.automotiveforums.com/vbulletin/showthread.php?t=510837&page=2&highlight=DOCTORBILL+Throttle

Its on the second page half way down. Showes from the bottom what the fast idle valvle looks like