: Idles rough after being started in the morning



29Roadster
10-01-09, 09:25 PM
1994 STC

Over the Summer I have performed several repairs and general maintenance.
Water pump replaced, spark plug wires, spark plugs, two ignition coils, coolant replaced, etc.

All was running well, until recently when gradually over a couple of weeks time the engine began to run rough after being started in the morning or after setting for more than an hour. It smoothes out after 20 seconds and runs smooth afterwards. I have noticed gas mileage has slipped slightly.
Any ideas
:hmm:

Submariner409
10-01-09, 09:32 PM
What engine ?

Two ignition coils replaced sounds like early Northstar.

What wires, plugs, coils ?

Do some searching for FPR - Fuel Pressure Regulator - for just those symptoms.

Ranger
10-02-09, 12:10 PM
Coolant levels and temperatures holding constant?

29Roadster
10-03-09, 01:10 PM
Temp appears to be holding (198-207) and with the help of a small ruler to check the level it appears to have lowered a little over a 1/4" over the past week or so. But I was losing coolant before the current rough idle appeared.

V-Eight
10-03-09, 01:15 PM
Has it been getting cold in the morning?

29Roadster
10-03-09, 02:03 PM
Temps have been in the low 60's at night and low 70's during the day. Perfect really.

V-Eight
10-03-09, 03:40 PM
Ok I was gonna say, if it was getting below 0 at night...not sure what that is in F, it could have just needed to warm up. I know my car runs rough for a few mins until it warms up in the winter.

29Roadster
10-03-09, 05:23 PM
was getting below 0 at night...not sure what that is in F, it could have just needed to warm up.

That would be 32F and it never gets that cold here, I'm in the San Francisco area. No it idles rough for a short time, then smooths out. I'm guessing it may be either something to do with a censor or in the fuel system. But I'm just guessing.

29Roadster
10-03-09, 07:07 PM
New info:(

I just took the Eldorado out to run a short errand; I noticed that at 45 mph the tach displayed 2000 rpm in overdrive. Then on the way back the tachometer showed the engine running at 3100 rpm while running at 45 mph (72kph)! I got home and parked the car.

Ranger
10-03-09, 09:41 PM
Keep a close watch on the coolant level. Rough idle at start up and coolant usage are initial head gasket symptoms.

29Roadster
10-06-09, 02:32 AM
Any ideas on teh high rpm?
Trans?

Krashed989
10-06-09, 04:37 AM
High rpm at that speed sounds like your TCC (Torque Converter Clutch) failed to engage. That would usually throw a code. Check the codes by pressing and holding the OFF and warmer (red) buttons at the same time until the whole dashboard lights up (key in the "on" position with or without the engine running). It will then tell you the codes and finish with "PCM?" At that point you can either press the OFF button once again to have it repeat the codes or you can turn the key off to exit diagnostics mode. Post your codes up here and we will help you.

Ranger
10-06-09, 12:32 PM
TCC would only raise the RPM by about 200. Not sure what is causing that kind of an RPM increase.

Submariner409
10-06-09, 12:43 PM
Those 45 mph engine speeds look like both a 4th gear engagement/TCC issue.

The TCC rpm drop upon engagement/disengagement (brake tap) is on the order of 300 rpm +/-.

4th is one pressure control, TCC is the solenoid, and the 1-2 and 2-3 shifts are a different set of solenoids.

eyekandyboats.inc
10-07-09, 02:06 PM
hey sub i got a question semi related to the TCC.
before my TCC went out at 130 Km/h ( 81 mph i think) the rpm was at 2600 or so.
now that my TCC is gone and i see the slippage. i only see the slippage from any where from 80-120 after that or so. my rpm at 130 km/h is exactly the same!! so i was wondering does the tcc disengauge after a certain speed?

Submariner409
10-07-09, 02:38 PM
Depends: TCC is a sort of mid-load flat road "overdrive" function which couples the torque converter input and output shafts together, thus eliminating all or most of the last n-th degree of slip.

If you increase engine load (accelerate or go up a hill) the TCC drops out as it is not designed to carry high torque loading, so it's entirely possible that you would see an rpm variation.

I can tell you from experience that TCC is not engaged at 130 mph.....:cool:

Ranger
10-07-09, 05:48 PM
Depends: TCC is a sort of mid-load flat road "overdrive" function which couples the torque converter input and output shafts together, thus eliminating all or most of the last n-th degree of slip.

If you increase engine load (accelerate or go up a hill) the TCC drops out as it is not designed to carry high torque loading, so it's entirely possible that you would see an rpm variation.

I can tell you from experience that TCC is not engaged at 130 mph.....:cool:
How could you tell?

Submariner409
10-07-09, 08:04 PM
TPS at 95%, MAP (manifold vacuum) at nearly 0, engine load at 94%. .........and not enough time/eyes/reaction time to watch for a 300 rpm drop. My speed limiter kicks in at 132 mph GPS, so when that happens engine loads go haywire from the injector drops, and I'd rather not run the risk of holing a piston from lean mixture changes.

But TCC will come in as the speeds get below 100 with lighter load on the transmission - it just takes a lot more road to figure the in/out points than I have at my disposal.............Some lucky dude in west Texas can figure the upper limits of the feature, not I.

Even under some pretty light loads you can see TCC come and go in hilly country with only partial throttle openings - WOT kills it entirely.

29Roadster
10-17-09, 01:45 PM
Update:

The problem with high RPMs while driving at 45mph has been resolved. The issue was a defective solenoid valve that controlled 3rd & 4th gears. Both solenoid valves were replaced with new units and the car now drives as it should.

Submariner409
10-17-09, 03:02 PM
29, Thanks for the update - we sort of ruined your thread :shhh:.

29Roadster
10-18-09, 01:15 PM
Once last note.

My mechanic removed the spark plugs and inspected each cylinder with a pencil sized video camera. Unfortunately he found coolant in cylinders 6 & 8. However he services a lot of Caddies (did 5 that week) and felt that since the car ran fine, better in fact than some of the others he serviced recently, that I should just drive the car and add coolant when needed. Repairs here in the San Francisco area would far exceed the value of the car.

Ranger
10-18-09, 05:05 PM
It will slowly get worse and at some point you will have to make a decision.

29Roadster
10-18-09, 06:03 PM
My decision is already made. Once it gets to the point were I can longer operate the car, I will buy another car maybe a 2002 Eldorado.

tateos
10-19-09, 12:37 PM
My decision is already made. Once it gets to the point were I can longer operate the car, I will buy another car maybe a 2002 Eldorado.

Sounds like a good plan - even the 2002s are getting to be pretty reasonably priced nowadays.

Submariner409
10-19-09, 01:56 PM
If you're seriously considering a 2002+, take a look at the 2002.5 (door sticker build date after 01/02 (Jan 02)) and later STS. All the latest running changes and Magnetic Ride Control, which was not optioned on the ETC.

29Roadster
10-20-09, 02:30 AM
My 94 still runs well and rides smooth. When it comes time to do something, I'll seriously look at a 2002 Eldorado.

robhersch
10-21-09, 03:34 AM
Once last note.

My mechanic removed the spark plugs and inspected each cylinder with a pencil sized video camera. Unfortunately he found coolant in cylinders 6 & 8. However he services a lot of Caddies (did 5 that week) and felt that since the car ran fine, better in fact than some of the others he serviced recently, that I should just drive the car and add coolant when needed. Repairs here in the San Francisco area would far exceed the value of the car.

An interesting ad on RX Auto Thermogasket (try the web) for some chemicals that are advertised for leak repairs, specific for N* engines.
I would be interested to hear if anyone has ever used it successfully although we do not now have any such problems or hopefully ever have the problem.

Ranger
10-21-09, 12:10 PM
It has been tried and does not work.