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4.9l Not idling right


epricedright

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On my 94 Deville 4.9l I'm having idle/throttle problems. No codes are showing up. I'm not sure if this problem occured right after I cleaned my throttle body out or not, but it's not acting right now. When I give it gas in park, it revs and then takes too long to go back to idle. When I'm driving along at say 20mph, i can let off the gas, and it keeps trucking along as if I'm still on the accelerator. When I come to a complete stop, it will then back down to normal. I read a post reply by bbobynski where disconnecting the ground for 30 sec. will reset the PCM to the default values for a clean throttle body...didn't help. What's causing this? Do I need to clean my throttle dujamaflopper (has the plunger that goes in & out that controls my idle)? Any ideas or thoughts?

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Your throttle blades or the throttle rod where the blades are bolted to sound like they are sticking. Not sure about the technical names but where the accelerator cable is hooked up to, if that rod gets any moisture on there it could corode and stick. It happened on our 1989 Fleetwood with a 4.5L.

Try spraying the outside of the throttle rod with some Silicone Lubricant. Using an oil such as WD-40 will attract dust and dirt. Give that a try see if that helps.

Spence

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Cool! Thanks Spence! That sounds simple...hope it works. I thought of that the other day and then brain farted and forgot to try it. I would have used a choke cleaner though. I'll try the silicone. Hope you're right as it's been a pain in the butt since it's been acting up.

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Cleaned the area where the accelerator cables are and the spring thing that goes into the throttle body w/ carb cleaner and sprayed the plunger wth silicone...no help. The ISC plunger seems to be controlling the deceleration...seems to be slower than normal...but maybe it's suppose to be as slow as it is??? The motor on the ISC that pushes the plunger in & out is working...hmmm :angry: Any other ideas?

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Have you checked the operation of the closed throttle switch on the ISC assembly???

Enter diagnostics and select the ECM mode. In ECM mode the "LO" icon on the climate control panel indicates the status of the closed throttle switch. It should be closed (icon on) whenever your foot is off the throttle. If not, then something is holding the throttle open or the switch has failed.

I would not lube anything as it will attract crud and in cold weather, it will turn to putty...

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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In the PCM mode ('94 is PCM, not ECM...I believe...there was no ECM mode), the "lo" icon is lit. Depress accelerator, it goes out. So that seems ok, but still no codes. What's up you think? Sitting still in park, shouldn't it go to idle speed right after lift off the accelerator? Cruisin around the neighborhood at 20mph, I can let off the accelerator and it acts if on cruise control, decelerating very slowly unless I come to a stop. If I don't come to complete stop, it will stay at that speed when I lift off the brake, it doesn't accelerate though This is my 1st caddy, so I'm not sure what to expect. Seems screwy and inefficient. Is this why they're gas hogs? ;)

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Sounds like the closed throttle switch is ok but it's too much of a coincidence that the problem started right after you cleaned the throttle body.

The system should learn the new idle value on it's own but in your original post, you said you disconnected the negative battery cable for 30 seconds. I would have thought the idle offset values would have been corrected. Inspect the throttle bore to make sure there isn't some crud holding it open slightly. Work the linkage by hand to make sure it isn't binding or sticking at the closed position. One member reported a burr on the bore. Resist the temptation to lube anything as the lube will turn to jelly in cold weather and cause binding. Not to mention that it will attract all kinds of crud.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I'm not for certain if this problem began before or after cleaning the throttle body. I cleaned & checked the throttle body really well, clean as a whistle. Everything seems to move freely, no sticking or binding. I guess by mistake I squirted some silicone on the ISC plunger, thinking that was sticking. The problem seems to lie with the ISC plunger or the motor that operates it as it appears to hold the throttle open too long. I'll look again in the morning and try to see exactly what's going on. Should the ISC not make any noise when I shut it off. Mine makes noises as it goes in & out right after I shut it off. Did that the day I bought it. I've noticed too, that sometimes it won't move or make any noise at all after shut off...go figure what that means...really frustrating.

There are two things that I've done that may have contributed to this possibly:

1. I detailed the motor...it was filthy. I had an oil leak, so I wanted to try and find that by getting the engine clean. I started off with a cold engine, I then double covered most everything that had wires going to it with aluminum foil ( including the ISC, MAT sensor, distributer, wiring harnesses, etc.), sprayed down the grimies with Castrol Super Clean and I then carefully pressure washed the engine compartment staying away from the spark plugs as much as possible. I then removed the foil and started the engine and let the hood down to dry it off, drove it around the block a couple times, then dried it off by hand including drying out the intake valleys that held water w/ paper towels. I then sprayed it down with STP protectant and then wiped it down real good. The dealer even said it would be ok as long as I was careful; in which I was. It ran for several days w/ no problems...regardless, I won't be putting water on this motor again.

2. I was inspecting for oil leaks and noticed a wire that was rubbing up against my CV boot, so I tried to put it back in it's little metal hook and it sparked when it touched it. Turns out the insulation was partly frayed away from rubbing against the boot and it grounded out against the metal hook. So I taped it up and secured it with a cable tie away from the CV boot. That wire was a heavy wire that ran from the battery to the alternator. So maybe one of those 2 things may be contributing to my problems??

I want to try and eliminate the ISC if possible. Should I first do the idle learn. Then take apart & clean the ISC (no lube). Then buy a new ISC if that doesn't help. So what's the procedure in removing, cleaning and replacing the ISC? Anything tricky w/ the ISC disassembly? Is it simple & straight forward? Do I need to disconnect the battery first, then do something w/ the computer after putting it back in?

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I'm not for certain if this problem began before or after cleaning the throttle body. I cleaned & checked the throttle body really well, clean as a whistle. Everything seems to move freely, no sticking or binding. I guess by mistake I squirted some silicone on the ISC plunger, thinking that was sticking. The problem seems to lie with the ISC plunger or the motor that operates it as it appears to hold the throttle open too long. I'll look again in the morning and try to see exactly what's going on. Should the ISC not make any noise when I shut it off. Mine makes noises as it goes in & out right after I shut it off. Did that the day I bought it. I've noticed too, that sometimes it won't move or make any noise at all after shut off...go figure what that means...really frustrating.

There are two things that I've done that may have contributed to this possibly:

1. I detailed the motor...it was filthy. I had an oil leak, so I wanted to try and find that by getting the engine clean. I started off with a cold engine, I then double covered most everything that had wires going to it with aluminum foil ( including the ISC, MAT sensor, distributer, wiring harnesses, etc.), sprayed down the grimies with Castrol Super Clean and I then carefully pressure washed the engine compartment staying away from the spark plugs as much as possible. I then removed the foil and started the engine and let the hood down to dry it off, drove it around the block a couple times, then dried it off by hand including drying out the intake valleys that held water w/ paper towels. I then sprayed it down with STP protectant and then wiped it down real good. The dealer even said it would be ok as long as I was careful; in which I was. It ran for several days w/ no problems...regardless, I won't be putting water on this motor again.

2. I was inspecting for oil leaks and noticed a wire that was rubbing up against my CV boot, so I tried to put it back in it's little metal hook and it sparked when it touched it. Turns out the insulation was partly frayed away from rubbing against the boot and it grounded out against the metal hook. So I taped it up and secured it with a cable tie away from the CV boot. That wire was a heavy wire that ran from the battery to the alternator. So maybe one of those 2 things may be contributing to my problems??

I want to try and eliminate the ISC if possible. Should I first do the idle learn. Then take apart & clean the ISC (no lube). Then buy a new ISC if that doesn't help. So what's the procedure in removing, cleaning and replacing the ISC? Anything tricky w/ the ISC disassembly? Is it simple & straight forward? Do I need to disconnect the battery first, then do something w/ the computer after putting it back in?

When the ignition is turned off, the ISC will set up for the next start. It should not ratchet.

Open the throttle slightly and depress the closed idle switch. The ISC plunger should retract. When the ISC plunger is fully retracted, disconnect the electrical plug from the ISC motor. There should be about .060 clearance between the throttle lever and the isc motor lunger when the plunger is fully retracted and the throttle is at rest. If not, adjust the plunger to obtain .060" clearance.

Take the car for a test drive and then recheck the ISC to make sure you have the .060" clearance with the engine idling in park. If the ISC ratchets, turn it out 1/2 turn and road test/examine for clearance.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Do I "open the throttle slightly and depress the closed idle switch. The ISC plunger should retract. When the ISC plunger is fully retracted, disconnect the electrical plug from the ISC motor." Do this with the engine OFF or ON? When you say depress the closed idle switch, you mean push in the plunger with my hand, right?

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OK...the plunger does NOT retract with the engine off, key on. With engine on, It does retract, while I simultaneously depressthe throttle lever, unplugged the ISC, turned the plunger out half turn to get .060 clearance. When it's fully retracted, there's a big clearance while holding it in, and when I let go, the spring will slightly push it out and that's when I get the .060 between the plunger and throttle lever - that's with it unplugged. I'm assuming that slight freeplay with the spring is normal??? I then test drove and it runs like it should...great...no decelleration probs. So what's that mean? Bad ISC? Now that it's unplugged I get codes 026(shorted throttle signal switch) & 052 (PCM memory reset)...no codes previously. That's a relief as I was concerned the OBD1 was not working possibly as I've had no errors codes till now.

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Yep, it's not decellerating right. It's gotta be that ISC. There's no clearance now either between the ISC & throttle lever. Should I try to run the plunger in w/ engine on in park and try to get that .060 clearance? Before with the plunger fully retracted, I had the clearance, but now that it's plugged back in, the plunger is pushed hard against the throttle lever.

Good thing I have these next 2 weeks off! :D

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You need to hold the throttle linkage open so you obtain a high idle and then depress the closed throttle switch. That will fool the computer and it will retract the ISC plunger to attempt to get the idle down. Don't release the throttle linkage until the plunger has fully retracted AND you have unplugged the electrical connection to the ISC motor. You may need a second set of hands. :lol: It is at this point that there should be .060" clearance between the plunger and the throttle mechanism. If not, adjust the plunger until the throttle bore is closed AND there is .060" clearance to the plunger. The engine should be idling very low at this point...

When you plug the ISC back in, it should contact the linkage to raise the RPM to a normal idle so the engine does not stall.

If after going through the adjustment, and it still doesn't work, you may need to replace the ISC motor assembly. You'll still need to adjust the new ISC motor though.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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That's exactly what I did, and after plugging it back in, the clearance was gone(the plunger up to the throttle lever was really tight) and the plunger is just moving way to slow...there's gotta be something wrong with that ISC.

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there's gotta be something wrong with that ISC.

the noises like khrrrr, prrr,frrrr, trrrr are the best indication of bad ISC motor.

:D

The saddest thing in life is wasted talent

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That's exactly what I did, and after plugging it back in, the clearance was gone(the plunger up to the throttle lever was really tight) and the plunger is just moving way to slow...there's gotta be something wrong with that ISC.

The ISC is supposed to tough the linkage when it is plugged in. The clearance adjustment is just for the initial alignment. If the ISC did not touch the linkage, the idle speed would be way too low and the car would stall.

Try backing off the ISC a half turn at a time to see if that corrects the problem.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I now understand what you meant regarding the clearance once plugged back in...makes sense. It's still making all those noises adallak described and it seems to retract way to slow. I have a new one coming from adallak, so I'll let you know if that helps. Thanks KHE and adallak for all your help...Appreciate it!

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