Idle Problems - '93 Touring Coupe w/ Northstar

[nyounce]

Live at 4500' feet. Engine idles at 1200 rpm. When I press on the accelerator and rev the engine up to 2000+ it takes 5+ seconds to return to 1200 rpm. Checked all the vacuum lines, replaced all intake manifold gaskets, and accomplished the TP Sensor/Idle Learn procedure to no avail. What next?

[kev2]

I am going to look for some info, high alt and idle problems ring a bell.

But some general quick checks would help, have you tried to access codes, Checked the mechinical linkage for any binding, have you cleaned the TB and ISC?

IMPORTANT let us know any modifications, add on's or use of afterrmarket parts.

[jackc]

The delay in returning to idle sounds like a problem with the ISC.

There's a PCM override that lets you retract the ISC plunger for testing. PS03, I think.

Could also be due to binding.

Pull the air duct off and watch the throttle plate while you work it. Does it move freely and close completely?

There is also supposedly a "hidden" idle set screw on 93's. I think I saw it when I had mine apart, on the bottom side of the throttle body. I'll check my FSM and report back.

[growe3]

With the engine off, observe the Idle Speed Control plunger, it should not touch the throttle linkage, check by wiggling the plunger a little.

Turn on the ignition, the ISC plunger should now be pressing against the throttle linkage, check by wiggling the ISC plunger, it should be very hard to move. If both check are Yes, I would next clean the Throttle Body.

Cleaning the Throttle Body:

Deposits in the Throttle Body can/will prevent the throttle plate from closing properly.

Use a can of spray CARBURATOR cleaner to clean.

With the engine OFF.

OBSERVE:

Remove the air filter tube to the Throttle Body.

Look into the Throttle Body bore, us there any obvious dark deposits build-up?

Pull the throttle plate open with the throttle cable, and look deeper into the Throttle Body.

To Clean:

CAUTIONS:

Place a few rags around and under the throttle body, to catch excess cleaner.

Be very careful to not let any over-spray get on your paint; instant meltdown

ACTIONS:

Use a can of spray CARBURATOR cleaner to carefully spray the exterior of the Throttle Body clean, be sure to get all of the side where the shaft comes out, towards the rear of the engine.

Open the Throttle Body and spray it clean. Don’t over do it. Spray a little, wait a few second the spray again to rinse off heavy deposits.

REMOVE THE RAGS!

START the engine, let it stabilize.

Gently rev the engine, while spraying more cleaner into the Throttle Body, to make sure the throttle plate is completely clean.

Throttle Body should be clean metal all over, all linkage parts should be clean and free of deposits.

Allow to idle, speed should be around 700 –800 RPM.

[nyounce]

With the engine off, observe the Idle Speed Control plunger, it should not touch the throttle linkage, check by wiggling the plunger a little.

Turn on the ignition, the ISC plunger should now be pressing against the throttle linkage, check by wiggling the ISC plunger, it should be very hard to move. If both check are Yes, I would next clean the Throttle Body.

Cleaning the Throttle Body:

Deposits in the Throttle Body can/will prevent the throttle plate from closing properly.

Use a can of spray CARBURATOR cleaner to clean.

With the engine OFF.

OBSERVE:

Remove the air filter tube to the Throttle Body.

Look into the Throttle Body bore, us there any obvious dark deposits build-up?

Pull the throttle plate open with the throttle cable, and look deeper into the Throttle Body.

To Clean:

CAUTIONS:

Place a few rags around and under the throttle body, to catch excess cleaner.

Be very careful to not let any over-spray get on your paint; instant meltdown

ACTIONS:

Use a can of spray CARBURATOR cleaner to carefully spray the exterior of the Throttle Body clean, be sure to get all of the side where the shaft comes out, towards the rear of the engine.

Open the Throttle Body and spray it clean. Don’t over do it. Spray a little, wait a few second the spray again to rinse off heavy deposits.

REMOVE THE RAGS!

START the engine, let it stabilize.

Gently rev the engine, while spraying more cleaner into the Throttle Body, to make sure the throttle plate is completely clean.

Throttle Body should be clean metal all over, all linkage parts should be clean and free of deposits.

Allow to idle, speed should be around 700 –800 RPM.

[jackc]

Here's the idle diagnostics from the FSM

[nyounce]

Here's the idle diagnostics from the FSM

Thanks for the chart. I'm going to spend some more time on the problem this morning. Yesterday, I took the ISC off; opened it up and lubricated the gears, and ran some 2000 grit paper through the points. While I was there, I increased the idle speed to 2000 rpm and returned the plunger to a fully retracted position; pulled the plug, and then unhooked the battery for 5 minutes. I was hoping that doing that would reset the whole system. When I started the engine, it still idled at 1200 rpm and had slow return to idle speeds from higher rpms. When I turned off the ignition, the ISC ratcheted about 20 clicks, after the engine had stopped.

One thing I did notice was that when both the ISC and Cruse Control were disconnected or removed the engine still idled at 1200 rpm, instead of the 450-600 rpm that I had expected. I have replaced the intake manifold gaskets and checked the associated hoses. Can you suggest a sure way to check for vacuum leaks?

[nyounce]

Here's the idle diagnostics from the FSM

Thanks for the chart. I'm going to spend some more time on the problem this morning. Yesterday, I took the ISC off; opened it up and lubricated the gears, and ran some 2000 grit paper through the points. While I was there, I increased the idle speed to 2000 rpm and returned the plunger to a fully retracted position; pulled the plug, and then unhooked the battery for 5 minutes. I was hoping that doing that would reset the whole system. When I started the engine, it still idled at 1200 rpm and had slow return to idle speeds from higher rpms. When I turned off the ignition, the ISC ratcheted about 20 clicks, after the engine had stopped.

One thing I did notice was that when both the ISC and Cruse Control were disconnected or removed the engine still idled at 1200 rpm, instead of the 450-600 rpm that I had expected. I have replaced the intake manifold gaskets and checked the associated hoses. Can you suggest a sure way to check for vacuum leaks?

Later....

Checked and found that the throttle cable was holding the butterfly valve slightly open. Can't get enough slack in the throttle cable to allow the valve to close fully. Is there a way to adjust the cable to effectively lengthen it?

[Ranger]

This might sound stupid, but check you floor mat to be sure it is not interfering with the pedal.

While I was there, I increased the idle speed to 2000 rpm and returned the plunger to a fully retracted position; pulled the plug

After this point, adjust the plunger to a .060 gap with the throttle linkage (after you get the cable thing figured out).

Ratcheting is a sign that the ISC motor is failing.

[nyounce]

This might sound stupid, but check you floor mat to be sure it is not interfering with the pedal.

While I was there, I increased the idle speed to 2000 rpm and returned the plunger to a fully retracted position; pulled the plug

After this point, adjust the plunger to a .060 gap with the throttle linkage (after you get the cable thing figured out).

Ratcheting is a sign that the ISC motor is failing.

Didn't get a chance to work on the car, today, but will start in the morning by clearing all the existing codes and seeing what codes come up with my current problem. Will also try to see if I do have a throttle cable problem. Is it possible that the '94 models had a different bracket to attach the throttle cable and cruise control unit to the TB. My bracket doesn't seem to fit quite right as I had to install a 3/16th spacer under the left side of the bracket, where the two 10mm bolts fasten the assembly over the point where the three vacuum lines are attached to the TB. I no longer have the '93 TB to make a comparison.

As far as the ratcheting goes, I don't ever remember the ISC making that noise, until it just began clicking about 20 times after each shutdown.

[jackc]

The trottle plate should be closed, except for whatever opening is given by the ISC, at idle.

Something's not right with the bracket. It should hug the throttle body - top and bottom - when you slide it over the TB. You may want to pull the manifold and do a bench inspection of how all of the stuff fits together.

As for the cables, did you hear them click into place when they fully seated into the groove? If not, that could be the 1/8th inch you're looking for.

I had to do kind of a dance to get my cables reinstalled. I had the manifiold in place but not bolted down, and the bracket was in position but not bolted in. Feed the throttle cable through the bracket. Stick a block of wood or something else soft into the TB to hold the plate open. Then feed the throttle cable back into the groove and pull on it to seat the bead into its notch. Then you can bolt the bracket to the TB. You'll have to lift the manifold to install the bottom bolts to the TB. Now verify that the throttle plate has full range of motion and does not bind. Once you've verified that the throttle cable works correctly, install the cruise cable. Verify again. Now you can bolt down the manifold.

As for the ISC, it will over extend if the Throttle Position Sensor is not connected and you will hear loud ratcheting - yes, about 20 times. Verfiy that the TPS is connected and working properly. Its on the side of the throttle body toward the front of the car.

[nyounce]

The trottle plate should be closed, except for whatever opening is given by the ISC, at idle.

Something's not right with the bracket. It should hug the throttle body - top and bottom - when you slide it over the TB. You may want to pull the manifold and do a bench inspection of how all of the stuff fits together.

As for the cables, did you hear them click into place when they fully seated into the groove? If not, that could be the 1/8th inch you're looking for.

I had to do kind of a dance to get my cables reinstalled. I had the manifiold in place but not bolted down, and the bracket was in position but not bolted in. Feed the throttle cable through the bracket. Stick a block of wood or something else soft into the TB to hold the plate open. Then feed the throttle cable back into the groove and pull on it to seat the bead into its notch. Then you can bolt the bracket to the TB. You'll have to lift the manifold to install the bottom bolts to the TB. Now verify that the throttle plate has full range of motion and does not bind. Once you've verified that the throttle cable works correctly, install the cruise cable. Verify again. Now you can bolt down the manifold.

As for the ISC, it will over extend if the Throttle Position Sensor is not connected and you will hear loud ratcheting - yes, about 20 times. Verfiy that the TPS is connected and working properly. Its on the side of the throttle body toward the front of the car.

The throttle plate is slightly open, even with the ignition off. If I disconnect the throttle cable, it snaps to fully closed. Both beaded ends of the cable are snug and snapped up against their stops, but the bracket that attaches them to the TB still requires a spacer on the left side to bring it into a level position. Additionally, the third 10mm bolt, on the side of the bracket, just barely catches the end of the notch that slides under it to secure the piece. I'm going to see if I can get a close look at how it should all fit together at one of the local dismantlers.

I haven't tackled the TPS, since it was on the manifold when I purchased it and was never disturbed. I'll see if I can find a method of checking it. When I ran the test to check the ICS, it lighted the appropriate lights to indicate when the internal points were making contact.

[jfreezn]

The slow return to 1200 rpm sounds like a vacuum leak to me. One often missed is the vacuum line to the brake booster. the booster could have a crack in it. check for vacuum leaks again.

Good luck,

Jim in Phoenix

Live at 4500' feet. Engine idles at 1200 rpm. When I press on the accelerator and rev the engine up to 2000+ it takes 5+ seconds to return to 1200 rpm. Checked all the vacuum lines, replaced all intake manifold gaskets, and accomplished the TP Sensor/Idle Learn procedure to no avail. What next?

[MAC]

Checked and found that the throttle cable was holding the butterfly valve slightly open. Can't get enough slack in the throttle cable to allow the valve to close fully. Is there a way to adjust the cable to effectively lengthen it?

Perhaps the throttle cable has disengaged with the retaining bracket. This problem was mentioned in a NHTSA recall buletin for the 1994 model Seville and Eldorado with manufacture dates of June 1993 through August 1993. However, I do not believe it was a recall in '93. I suspect you may nevertheless be experiencing the same problem?

I suggest inspecting the throttle cable to make sure it's properly seated in the retaining bracket and, if necessary, install a cable tie to secure the cable.

[nyounce]

Checked and found that the throttle cable was holding the butterfly valve slightly open. Can't get enough slack in the throttle cable to allow the valve to close fully. Is there a way to adjust the cable to effectively lengthen it?

Perhaps the throttle cable has disengaged with the retaining bracket. This problem was mentioned in a NHTSA recall buletin for the 1994 model Seville and Eldorado with manufacture dates of June 1993 through August 1993. However, I do not believe it was a recall in '93. I suspect you may nevertheless be experiencing the same problem?

I suggest inspecting the throttle cable to make sure it's properly seated in the retaining bracket and, if necessary, install a cable tie to secure the cable.

I have most of my problems solved, now, thanks to all the help I've received form you guys. The major problem turned out to be a difference in the physical layout of the bracket that receives the throttle cable on the '93 and '94 models. The '94 bracket positions the end of the cable approximately 1/8 of an inch farther away from the TB, forcing the valve to open slightly more at idle. I guess the old adage that "If you hear hoof beats, you should expect to see horses, not zebras" applies. Should have noticed that!

[The_Raven]

Checked and found that the throttle cable was holding the butterfly valve slightly open. Can't get enough slack in the throttle cable to allow the valve to close fully. Is there a way to adjust the cable to effectively lengthen it?

Perhaps the throttle cable has disengaged with the retaining bracket. This problem was mentioned in a NHTSA recall buletin for the 1994 model Seville and Eldorado with manufacture dates of June 1993 through August 1993. However, I do not believe it was a recall in '93. I suspect you may nevertheless be experiencing the same problem?

I suggest inspecting the throttle cable to make sure it's properly seated in the retaining bracket and, if necessary, install a cable tie to secure the cable.

I have most of my problems solved, now, thanks to all the help I've received form you guys. The major problem turned out to be a difference in the physical layout of the bracket that receives the throttle cable on the '93 and '94 models. The '94 bracket positions the end of the cable approximately 1/8 of an inch farther away from the TB, forcing the valve to open slightly more at idle. I guess the old adage that "If you hear hoof beats, you should expect to see horses, not zebras" applies. Should have noticed that!

Very interesting... Is the engine original?