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1991 Cadillac Sedan deVille
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Discussion Starter #1
'91 DeVille - I have noticed recently that when I restart the car after it has been turned off for about 30 minutes, it will idle up, then it will do way down, jump way up, then way down (almost stall), then back up, etc. It only does this on "hot" start-up. When I turn it off that little thing on the front of the motor "ratchets" back and forth. I think I was told this was the idle control valve or something? I wonder if that thing is going bad? Also my car is not idling as smooth as it should be. It has new injectors and plug wires. It has that knock I have mentioned. I would like to clean those EGR tubes, but not sure how, or if problem is related.

Any ideas?

Thanks!
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,261 Posts
'91 DeVille - I have noticed recently that when I restart the car after it has been turned off for about 30 minutes, it will idle up, then it will do way down, jump way up, then way down (almost stall), then back up, etc. It only does this on "hot" start-up. When I turn it off that little thing on the front of the motor "ratchets" back and forth. I think I was told this was the idle control valve or something? I wonder if that thing is going bad? Also my car is not idling as smooth as it should be. It has new injectors and plug wires. It has that knock I have mentioned. I would like to clean those EGR tubes, but not sure how, or if problem is related.

Any ideas?

Thanks!
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I was told this was the idle control valve or something?
ISC - Idle Speed Control motor -

not unusual for it to fail -

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check the fuel pressure - post the results -
key-on - engine off -
then with the engine running at idle -

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to clean the EGR tubes in the base of the TB -
spray them with carb cleaner -
and GENTLY poke with a steel wire/coat hanger -
to break up the carbon -

if really bad - use a drill bit - BY HAND -
 

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White Diamond '03 DHS (with DTS floor shift)
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Look down the TB. If the EGR tubes are carboned closed like the picture below, rod them out.

Also look for a vacuum leak.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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I would have thought the cheap easy stuff would have been taken care of before buying parts. By all means clean those EGR tubes and verify ISC adjustment and proper function. Check for broken vacuum lines too.
 

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1991 Cadillac Sedan deVille
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Discussion Starter #5
Well that is my mechanic for you. (rolleyes). Looks like I will be trying to clean some EGR tubes this weekend.

Thanks.
 

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1991 Cadillac Sedan deVille
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If your issue still exists after doing all the suggested things, go out there and check the injectors. I know you recently had them replaced, but you never know (they were used). When the engine is hot and the problem occurs, shut the engine off and Ohm the injectors. Record all the values and make sure they're within 12-18 Ohms. Even if all of the injectors check out resistance wise, start the engine and listen to each of them with a stethoscope or a screwdriver to your ear.

One or more inoperative injectors will cause similar idle problems. The engine will misfire and the idle will go down, the computer will step in trying to stop the engine from stalling and will raise the idle (through the ISC), then the engine fires the "healthy" cylinders and the idle goes too high, so now the computer commands less throttle; that keeps going on and on forever. Some injector issues could even explain the knocking issue you've had for awhile (the cylinders with no injector flow will run hotter and put extra load on the rest of the cylinders).
 

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1992 DeVille
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One or more inoperative injectors will cause similar idle problems. The engine will misfire and the idle will go down, the computer will step in trying to stop the engine from stalling and will raise the idle (through the ISC), then the engine fires the "healthy" cylinders and the idle goes too high, so now the computer commands less throttle; that keeps going on and on forever.
extremely well put. I think this is my issue...

I will investigate
 

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1991 Cadillac Sedan deVille
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Discussion Starter #8
Thanks. Well oddly enough the car has stopped doing this. I still want to check those EGR tubes this weekend.

Yes, it is true I did replace the injectors. All 8 of them only 4000 miles ago. It cost me over $300.00 and they were "completely rebuilt" and have a 5 year warranty. If it is the injectors, I will not deal with that again. I mean I know the injectors will be replaced for free, but I am not dealing with the labor of it. I have spent about all of the money on this car that I really care do and about to move on. I dont mind doing anything minor/inexpensive at this point, but the car is not worth it to me anymore to put alot of $ into it. I have about $2500 in it (and have only put 4k miles on it), advertised for $1950 and no serious buyers. I am not pushing the sale of it, but I do have it for sale. I had thought about just keeping it as an extra car, but I don't know. I guess it depends. I MUST put brakes on it this weekend... that is next on the list, I cannot wait another week on those.

Thanks.
 

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1991 Cadillac Sedan deVille
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It's not that hard to replace the injectors yourself (if that's what needs to be done). There is a detailed thread about the work needed. Look it up in the forum.

Also, keep in mind that injectors never really get rebuilt. You can't disassemble injectors and change things inside like the coil or pintle. What so called injector rebuilders do is change the o-rings and filters (if equipped), hook the injectors to a cleaning machine, and then flow test and match them.
 

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1992 DeVille
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mc_marto said:
It's not that hard to replace the injectors yourself (if that's what needs to be done). There is a detailed thread about the work needed. Look it up in the forum. Also, keep in mind that injectors never really get rebuilt. You can't disassemble injectors and change things inside like the coil or pintle. What so called injector rebuilders do is change the o-rings and filters (if equipped), hook the injectors to a cleaning machine, and then flow test and match them.
So how would that change the lowering impedance of failing injectors??

Also I remember saving the link to that's injector replacement thread, but isn't t true you have to take off/slightly move the ps pump to get the fuel rail off?
 

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So how would that change the lowering impedance of failing injectors??

Also I remember saving the link to that's injector replacement thread, but isn't t true you have to take off/slightly move the ps pump to get the fuel rail off?
So how would that change the lowering impedance of failing injectors??

It won't. The Bosch injectors, however, are known to have better coil design/insulation and failing coils with them is rare.

Also I remember saving the link to that's injector replacement thread, but isn't t true you have to take off/slightly move the ps pump to get the fuel rail off?

True, but that's not a big deal. I know things we haven't done can many times be intimidating and discouraging, but they are often times not as hard as they seem.
 

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mc_marto said:
So how would that change the lowering impedance of failing injectors?? It won't. The Bosch injectors, however, are known to have better coil design/insulation and failing coils with them is rare. Also I remember saving the link to that's injector replacement thread, but isn't t true you have to take off/slightly move the ps pump to get the fuel rail off? True, but that's not a big deal. I know things we haven't done can many times be intimidating and discouraging, but they are often times not as hard as they seem.
Right on man thanks for the vote of confidence! I'm planning on getting a set of flow matched Injectors and when I have time I'll swap em and check for leaks. I listened to all mine and they all sound steady. Every once in a while my car has a hiccup like you described at idle where the isc will kick up a little and raise the idle a tiny bit.

One injector was ticking louder than the others. I have to get an ohm meter to check them when hot, but that's next up.
 
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