[onelove6366]

I have a 98 Deville Concours 211,000 miles. Back in June 2012 after driving around all day in stop and go traffic RPM's started running very high and the car was pulling without me using the gas. I had to stand on the brakes to get it to stand still. Pulled off and let it cool down a little while. Back then we added coolant or oil which turned out to be low and now we can't remember which one it was!

Over the weekend before and through Christmas Day I have put a little over 800 miles on the car. Some open road and some stop and go traffic driving. Monday evening the high RPM issue came back strong. Pulled into a gas station and added coolant oil and transmission fluid. All looked a little low. Got home fine however the Service Engine Soon light is on in the dash. Now it keeps doing it almost every time I start it.

When I start the car if it running high RPM's I shut it off and restart. Sometimes the RPM's will run normal after the first time but sometimes I have to turn it off and on several times before it does it. Sometimes the car runs normal the whole trip and sometimes the high RPM situation develops while I am driving.

We are losing coolant but can't find where. We are suspecting the hard cross over pipes at the back of the engine and have done this repair on another 98 Deville so we know what to do - just holding off because we aren't SURE - we can't SEE the coolant leaking from that area as we did with the other car so it's not certain that is the issue. Replaced the heater core earlier this year and just last month the upper and lower radiator hoses. No apparent leaks in the radiator so we haven't gone that route just yet. I am thinking I need to get a shop to pressure test but this worries me because I am fearful they will blow something out doing the test leaving me with no car to drive as my husband is in the middle of a major front end rebuild on our 2nd vehicle.

We are also losing oil - not a LOT and cannot pinpoint the source of that leak either. We keep close eyes on levels of both so there has never been a time when they ran low or out.

When I get stuck in really bad traffic that is stand still for a period of time, roll ahead a few feet, stand still again .... after a while of that the car starts running very poorly. I try to avoid this type of traffic to the point of just pulling over and waiting it out for a little while if I can.

I will pull the codes tonight and update this post with what it is reading but just wanted to throw this out to get your input (as I value it highly). Possible Throttle Position Sensor issue, EGR Valve, etc.?

This year we have replaced plugs and wires, alternator, new battery, blower motor and heater core. I get the oil changed with high mileage synthetic blend religiously. Nothing but premium gas either.

We do all of our own work despite my husband's complaints. Our bank book can't afford it and I really would prefer to KNOW what was done to my car rather then spend a lot of money and not be sure who did the work.

Can anyone provide any input at this point? Thanks!

 

[Ranger]

Code AND definitions will help greatly when you get them.

High idle could very well be a sticking throttle plate. When was the TB last cleaned?

Check the heater pipes you speak of. They are a common leak point. Coolant loss with no external leaks is not a good sign, but it's too early to go down that road. It might be a small leak that is evaporating before dripping. No overheating I presume?

 

[onelove6366]

No overheating. Oil is not foamy which would indicate head gasket problems. I've already thought of that.

Sticking throttle plate. Hmmm.... I have NO idea when the TB was last cleaned. My husband said he was reading in the service manual that you had to be very careful when cleaning because using a carb cleaner will damage the internal pieces. Is this true? It may be that it just needs cleaning but we want to make sure we don't damage it further in doing so.

Thanks Ranger!

 

[jounier11]

211,000K :cool2: has the HG ever been repalced/repaired or is it original stuff??!!?

 

[Ranger]

No overheating. Oil is not foamy which would indicate head gasket problems.

Wrong. Not on a Northstar. They rarely (if ever) put coolant in the oil when a HG fails.

Sticking throttle plate. Hmmm.... I have NO idea when the TB was last cleaned. My husband said he was reading in the service manual that you had to be very careful when cleaning because using a carb cleaner will damage the internal pieces. Is this true?

I've heard that (can't explain it), but I have used Gumout Carb cleaner for years until I finally used it up last year. Never had a problem. They do sell a dedicated TB cleaner though. Personally (from the smell) I think it is relabeled Brakleen.

 

[Ranger]

No overheating. Oil is not foamy which would indicate head gasket problems.

Wrong. Not on a Northstar. They rarely (if ever) put coolant in the oil when a HG fails.

Sticking throttle plate. Hmmm.... I have NO idea when the TB was last cleaned. My husband said he was reading in the service manual that you had to be very careful when cleaning because using a carb cleaner will damage the internal pieces. Is this true?

I've heard that (can't explain it), but I have used Gumout Carb cleaner for years until I finally used it up last year. Never had a problem. They do sell a dedicated TB cleaner though. Personally (from the smell) I think it is relabeled Brakleen. I think the manual says to do it once every 30K. I do mine every spring which makes it a simple spray and wipe operation.

 

[onelove6366]

Wrong. Not on a Northstar. They rarely (if ever) put coolant in the oil when a HG fails.


REALLY? I did not know this. What signs do you look for to know if there is a possibility the HG is failing? I can smell coolant so I am pretty sure it is leaking out from somewhere. We are suspecting the diaphragm is bad on the water pump and are planning to replace the water pump soon. My husband wants to also do the hard pipes at the same time since he has to tear it down that far. As I mentioned earlier though - his Ford Ranger truck is in our garage with the front end being rebuilt along with the clutch replaced and new muffler. It is taking a while partly due to my husband being a perfectionist and that his work schedule does not allow for much spare time to dedicate to the truck even though he is trying to make it a high priority so we can get the Caddy in. Oh, also the oil leaking is not real bad - it is just happening all the time so we keep a close eye on the level. I am real funny about making sure all the fluids are filled as they should be so I am slightly obsessive about checking them at least once a week. We can't see where it is coming from and neither can the guys who change the oil so it seems it's not a SCREAMING issue at the moment.


I've heard that (can't explain it), but I have used Gumout Carb cleaner for years until I finally used it up last year. Never had a problem. They do sell a dedicated TB cleaner though. Personally (from the smell) I think it is relabeled Brakleen. I think the manual says to do it once every 30K. I do mine every spring which makes it a simple spray and wipe operation.

My husband said he read in the service manual that the internals of the TB are coated with something that is designed to prevent buildup and using standard carb cleaner removes that coating. I will look into getting the dedicated TB cleaner and see if that helps.

 

[Ranger]

REALLY? I did not know this. What signs do you look for to know if there is a possibility the HG is failing?

Signs of a failing HG are unexplained coolant loss. Overheating (particularly under a load). Oily exhaust tips. Excessive exhaust steam above and beyond the normal condensate that smells sweet like coolant (only in the later stages).

Oh, also the oil leaking is not real bad

Not uncommon. Where exactly is it leaking? Front, rear, passengers side, etc. Might be a simple oil level switch, filter adapter or pressure switch. Wost case is a rear main or the half case seal, in which case you add oil and live with it (expensive repair).

My husband said he read in the service manual that the internals of the TB are coated with something that is designed to prevent buildup and using standard carb cleaner removes that coating. I will look into getting the dedicated TB cleaner and see if that helps.

Yeah, I've read that too. If you neglect the TB cleaning (and most people do), you'll be amazed at the amount of build up even with the "special coating". Like I said, I have used carb cleaner and never had a problem or noticed any coating being removed, for whatever that is worth. At the same time, I think TB cleaner is some pretty strong solvent as well from my observations, again for whatever that is worth.

 

[onelove6366]

Signs of a failing HG are unexplained coolant loss. Overheating (particularly under a load). Oily exhaust tips. Excessive exhaust steam above and beyond the normal condensate that smells sweet like coolant (only in the later stages).

Well - Based on this I would say I don't believe it is the HG even with the coolant loss issue we are experiencing right now. I am leaning towards the water pump nearing the end of its' useful life as I'm not having any of the other signs you list.

Not uncommon. Where exactly is it leaking? Front, rear, passengers side, etc. Might be a simple oil level switch, filter adapter or pressure switch. Wost case is a rear main or the half case seal, in which case you add oil and live with it (expensive repair).

We are still trying to pinpoint the area the leak is coming from. There is oil on the undercarriage (bottom of motor i guess you could say - I'm not that technical) but we are working on it. I sort of think it may be the seal but that is just my suspicion which unfortunately turn out to be accurate too much of the time so I am going with the add oil and live with it path.

Yeah, I've read that too. If you neglect the TB cleaning (and most people do), you'll be amazed at the amount of build up even with the "special coating". Like I said, I have used carb cleaner and never had a problem or noticed any coating being removed, for whatever that is worth. At the same time, I think TB cleaner is some pretty strong solvent as well from my observations, again for whatever that is worth.

Still haven't had time to pull the codes. Will try to do it today though. Our well pump went out so we have no water now as well. Went out to buy parts for the repairs yesterday evening and replacing it this afternoon. It's pouring at my house right now with one thing after the other! Thanks again Ranger - I have been reading these forums for quite some time and it doesn't take long to figure out who knows what they are posting about and who doesn't!

 

[onelove6366]

Signs of a failing HG are unexplained coolant loss. Overheating (particularly under a load). Oily exhaust tips. Excessive exhaust steam above and beyond the normal condensate that smells sweet like coolant (only in the later stages).

Well - Based on this I would say I don't believe it is the HG even with the coolant loss issue we are experiencing right now. I am leaning towards the water pump nearing the end of its' useful life as I'm not having any of the other signs you list.

Not uncommon. Where exactly is it leaking? Front, rear, passengers side, etc. Might be a simple oil level switch, filter adapter or pressure switch. Wost case is a rear main or the half case seal, in which case you add oil and live with it (expensive repair).

We are still trying to pinpoint the area the leak is coming from. There is oil on the undercarriage (bottom of motor i guess you could say - I'm not that technical) but we are working on it. I sort of think it may be the seal but that is just my suspicion which unfortunately turn out to be accurate too much of the time so I am going with the add oil and live with it path.

Yeah, I've read that too. If you neglect the TB cleaning (and most people do), you'll be amazed at the amount of build up even with the "special coating". Like I said, I have used carb cleaner and never had a problem or noticed any coating being removed, for whatever that is worth. At the same time, I think TB cleaner is some pretty strong solvent as well from my observations, again for whatever that is worth.

Still haven't had time to pull the codes. Will try to do it today though. Our well pump went out so we have no water now as well. Went out to buy parts for the repairs yesterday evening and replacing it this afternoon. It's pouring at my house right now with one thing after the other! Thanks again Ranger - I have been reading these forums for quite some time and it doesn't take long to figure out who knows what they are posting about and who doesn't!

PS: I don't know why my replies are within your quoted reply. Sorry!

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Note: This is in reply to Junior's post:

I don't know if it's been replaced or not. I know I am the 3rd owner. First guy died a few years ago. Second had the car for less than two years and now here I am. I have thought about contacting the Cadillac dealer whose emblem is on the back of the car to see if they have service records for the VIN number. Do you think they'd provide them? It may be useful information if they had it serviced there. We do all of our own work aside from oil changes and tires so if the previous owners were like us - there are no records. Car runs like a top notwithstanding these minor maintenance and use items that are really to be expected. Motor is strong and I have put it to the test for sure!

 

[onelove6366]

Pulled Codes - here it goes: Please let me know what you guys think about my high RPM problem in relation to these codes - related? Maybe in history it looks like but that just seems strange. Ranger - still think I should go with cleaning the throttle body? PS - these are the OBD II code definitions.

Codes 12/28/12:

PCM P0122 – History: Throttle Position (TP) Sensor Circuit Low Voltage
PCM P0603 – History: Control Module Long Term Memory Reset
PCM P1122 – History: Throttle Position (TP) Sensor Circuit Intermittent Low Voltage

No IPC

ACM B1312 – Current: High Side Temp Sensor Open Circuit
ACM B1341 – History: Air Mix Door Two Movement Fault - NOTE: We fixed this several months ago. I know more than 50 starts - shouldn't it clear automatically?

No SDM

TCS C1235 – History: Right Rear Wheel Speed Circuit Open or Shorted
TCS C1378 – Current: Exhaust Solenoid Valve Short to GND

No PZM

No IRC

No RFA

No CCP

No MSM

No MMM