1994 Seville SLS driving me insane

[Mike S.]

Since I've owned the car for about a year, I had a problem with the idle sticking sometimes around 1500 rpm, and running roughly every once in a while. Over the summer it started running a little rougher, and the idle jumped up to around 1000 rpm, so I cleaned the throttle body and replaced the air filter. This helped for a little while, but the problem with the idle sticking became a little worse, and I got the P080 code, or whatever the throttle angle high code is. I replaced the throttle position sensor, and the problem is way worse now. The idle is at 1000 rpm in drive with the brake on, but it jumps up to 1300-1500 when in nuetral or park. The car accelerates on it's own as well. My gas mileage has also been steadily declining over the past few months, and on my first tank of 80% in town driving since I replaced the sensor, I got 170 miles off the tank of gas. Any suggestions?

[BodybyFisher]

Have you disconnected the battery and allowed the system to re-learn? If I am not mistaken, the TPS must be adjusted but I am not sure about that on your year.

I think your year has an ISC Motor, Barry94 among others are very familiar with it, but Barry put this thread together check it out:

http://caddyinfo.ipbhost.com/index.php?sho...7605&hl=ISC

[KHE]

This sounds like a textbook idle speed controller case... do a search in the archives on "Idle speed control" and ISC and read up.

[The Fred]

Yea that stupid ISC can be a pain in the 838

On my 1990 Seville I had to calibrate the TPS and the ISC still acts up some times

[epricedright]

Yep....ISC. Check to make sure there is slack in your cruise linkage as well. Do you hear ratcheting noises coming from the ISC at shut down?

[The Fred]

Don't worry Mr. Mike.. you're in good hands with these folks.

They know almost everything about these motors.

Of course I've managed to cause a nearly unsolvable problem with my '94 STS but that's well in character for me

[Mike S.]

Yep....ISC. Check to make sure there is slack in your cruise linkage as well. Do you hear ratcheting noises coming from the ISC at shut down?

Yep, I do hear the ratcheting. Any idea on how much this part would cost? How hard is it to install? How do I go about calibrating the TPS? Thanks a ton.

[KHE]

Yep....ISC. Check to make sure there is slack in your cruise linkage as well. Do you hear ratcheting noises coming from the ISC at shut down?

Yep, I do hear the ratcheting. Any idea on how much this part would cost? How hard is it to install? How do I go about calibrating the TPS? Thanks a ton.

I think they are in the $75 to $100 range - others who have replaced their ISC will chime in with the exact cost. www.gmotors.com has OEM parts at wholesale prices. It is not difficult to instal and adjust. I would not mess with the TPS at this time - it is most likely fine.

[Ranger]

Installation is pretty straight forward when you look at it. Don't forget to adjust it after installation. With the engine idling, press on the plunger til it retracts. When it bottoms out, unplug it. The engine idle should drop to about 450 RPM or maybe die. Now adjust the plunger to a .030 gap with the throttle linkage. Plug it back in and you're set to go.

[epricedright]

I just looked at rockauto.com and they are $90 + shipping. Look under "Emissions". Like Kevin mentioned, gmotors has them as well. Easy to install and adjust.

[Mike S.]

I really appreciate the help guys. One more issue that has recently arose is an overheating problem with the AC on. This happened twice, so when I needed to go run a few errands today, I drove with the AC off, and the coolant temp was 234 degrees when I got back just now. I was going to try the thermostat first. Any other ideas as to what this might be?

[Cadillac Jim]

Overheating causes from the 1997 FSM, dignostic table on page 6-178:

• Make sure that the system holds pressure. After driving it, let it have a couple of hours to cool down, then remove the surge tank cap. There should still be pressure. If not, fix any leaks and get a new radiator cap from the dealer.
• Make sure that the coolant is at least 50/50, or protection to -34 F. If not, replace the coolant.
• Check the water pump belt tension. It's under a cover on the driver's side of the engine on the front bank. If it's not tight, I would replace the belt, the tensioner, and the water pump.
• Make sure that the thermostat bypass is working OK. This is important as it can mimic a stuck thermostat or head leakage. This is a hose that can be replaced.
• Make sure that the radiator fins are OK and unobstructed.
• Make sure that the fans are OK. Just turning on the A/C will cause them to come on at low speed. If they don't, then fix the electrical problem and/or replace the fans.
• Make sure that the radiator hoses aren't collapsed or blocked, and that the radiator still flows well.
• Make sure that the throttle body coolant flow is unobstructed.
• Last, check the thermostat.

From your main symptom, overheating in traffic with the A/C on but not off, I would check whether the fans are running first. It's simple, quick, and free, and it would explain your problem.