: 4.6 Northstar doining very strange

10-25-08, 03:06 AM
Hello everyone,

I am Ferdy and i live in the Netherlands. I just purchased a Cadillac Seville STS from 1993 with the Northstar V8. We don't have that much of these cars so there are very VERY litlle people here that know something about these cars and there engine. I hope someone can help me out.

The problem is that the engine idle's very rough. It doesn't mather if its hot or cold, he does it all the time. And when he is cold he sometimes goes too somewhere between 2000 - 3000 rpm whitout me touching the gas !!!

The next problem is when i drive about 40 mph and i want to speed up i give a bit gas and the hole car starts vibirate. But when i give some more gas it stops and he pulls normal.

What could be the problem? I allready read lots of forums but can't really finger out what is the problem. Please can't drive my Caddy like this :(

Any think can help!

10-25-08, 10:22 AM
How many miles on it? It may be due for plugs & wires. A/C Delco seem to perform the best. Also check for a vacuum leak and as always, start by pulling the DTC's (Diagnostic Trouble Codes).

10-25-08, 11:00 AM
The milage is about 140k And i don't know what that maintace has been.

I've allready pulled out the codes and they all came up as HISTORY CODE.

This are the codes i got from it:



I cleared all codes after that an than he sad no codes to have ad all.
After i drove about 30 miles i ran the OBD again and got again the P052 HISTORY and P109 HISTORY code. This should be the PCM memory reset and Keep alive memory (KAM) reset/PCM has lost primary battery power.

I don't know what it can be. I will chek for vac. leaks today and about the sparks and wires how can i test them? Becaus parts for cars from the USA are very expensive here in Holland, so if thats not the problem it will only cost me a lot of money.

Thansk for helping me !!!


10-25-08, 11:37 AM
It's hard to test the plugs, but for the wires, mist them with a spray bottle of water with the engine idling in the dark and watch for a light show. At that mileage it may be due for a tune up (plugs & wires).

10-25-08, 01:01 PM
Ok, i will try to look when it's dark.
I also took off the big plate the covers the intake manifold between the cilynders and it was a bit of a mess with a layer of oil covering the plastic manifold that light under neeth it. Could that also be a problem?

How and where do i check for vac. leaks? I try to look today but this engine is so masive and complecaded that i don't realy know where to look.

I've also read in another forum that the ERG valve or some other sensor could give this kind of problem. Where can i find this sensor and how can i cleen it?

10-25-08, 04:15 PM
There should be no oil under the silver beauty cover. Oil deteriorates rubber and thus is not good for the wires. Try to find the source and correct it. Check the PCV valve on the rear cam cover for starters. It might even be the source of a vacuum leak. Check all the vacuum lines and the manifold mounting bolts. A stethoscope would be a big help. In the absence of one, spray some Brakleen or such around any possible leak points and listen for an RPM increase.

The EGR valve is between the TB and the master cylinder. Looks like a black canister with an electrical connector on top. There is a tutorial on cleaning it in the Tech Tips section.

10-25-08, 07:09 PM
A good cleaning of the throttle body would help the idle. An old toothbrush does a nice job. Do not get carb cleaner on the mass air sensor.
Pull the spark plugs and inspect them. Report back to us what number they are. The proper Delco platinum are the best. Price a new set at www.rockauto.com.
Look for a Factory Service Manual on ebay. They can be had for $100 or so and is mandatory for proper service. It will pay for itself many times over.

10-27-08, 12:27 PM
Today a looked at my wires and plugs. The wires give lighting sparks to te engine blok so they need to be replaced. Is it nececery to buy ac delco? or can other be as good?
The kind of plugs that are in my car are from ac delco with number: 41-950.

I also looked at the ERG valve but that one is moving as it should be so i don't think that is the problem.

As far as the PVC valve, i don't know really where i can find it. And i don't know what the word starters meens. Could someone give me some more advice on that one?

I will try too look for some vac. leaks tomorow.
And i will take off the TB for a good clean.

My gas seems to bet stuck sometimes. The engine runs about 2500 - 3500 RPM whitout me touching the gas. Should i lubricate the gas cable and the moving parts on the TB?

Sorry for ALL the questions but your my only help in this issue

10-27-08, 12:51 PM
The wires give lighting sparks to te engine blok so they need to be replaced. Is it nececery to buy ac delco? or can other be as good?
There's your problem. A/C Delco wires seem to perform the best. That plug number is correct for your car.

As far as the PVC valve, i don't know really where i can find it. And i don't know what the word starters meens. Could someone give me some more advice on that one?

The PCV valve should be on the rear cam cover near the passengers side. It will have a vacuum line plugged onto it. By "starters" I meant "to begin with", Sorry for the confusion.

My gas seems to bet stuck sometimes. The engine runs about 2500 - 3500 RPM whitout me touching the gas. Should i lubricate the gas cable and the moving parts on the TB?
Cleaning the TB will solve this. No need to remove the TB to clean it. Don't lube the cable or any other parts. That will just cause them to collect dirt and get sticky. There is a tutorial on how to clean the TB in the Tech Tips section.

10-28-08, 08:58 AM
I justed cleanded out my TB. It was a bit dirty and my idle did get a bit better. But still not what i think is normal.
But as far i can look in to my intake manifold it looks very dirty too. Can this also cause any thing that make the idle go crazy?

And i allready had one time after i have cleand the TB that the RPM's go up to about 2500 whitout touching the gas. So did i not clean it right? or can something else be the problem? It looks very cleen to where i can reach.

10-28-08, 11:23 AM
An oily residue inside the manifold is normal. It is from the crankcase gases drawn in through the PCV valve and exhaust gases drawn in from the EGR valve, but should not affect the idle. Remove the top of the manifold. It's removable on the '93/'94. Turn the key on, but DO NOT crank the engine with the manifold cover off. See if any fuel leaks from the nipple on the FPR. If so, replace it. If the FPR is OK, then you might try adjusting the ISC (Idle Speed Control) motor. It should not have gotten out of adjustment, but would be worth a try. Perhaps it is going bad and needs replacement.

10-29-08, 03:52 PM
Dunno if u already got your spark plug wires replaced but here a url to a store in the Netherlands that is fair with there GM / acdelco parts
http://www.arton.nl (als je ze belt vraag dan naar Patrick G.)


11-02-08, 06:32 AM
Hello Ranger, and others,

Today i've did some things on my Cadillac to try to solve the problem.
I took of the TPS and looked if i could cleen it. I saw the was not posible so i puted evrything back together. When i fired it up tis straight went to 3000 RPM (again...). afther giving some gas my self it got back to about 1100-1200 RPM. Normaly it idle's about 900 RPM. And i can not get it lower than 1100 RPM.

I ran my code's again and got the next one:

P021 HISTORY Shorted TPS Signal [VCC]
P022 HISTORY Open TPS Signal [VCC]
P026 HISTORY Shorted Trottle Signal Switch
P070 HISTORY Intermittent TPS Signal

And when i turn of the ignition key the thing on the right side of the TB starts to knock an move fowards and than goes back to it normal position. He does dis about 5 times. The same is going on when i turn back on the ignition.
When i take of the TPS connector it does the same but more than 5 times and much faster.

Do you have an idea??? thanks allready

11-02-08, 09:13 AM
Apparently the Throttle Position Sensor is now out of adjustment. The motor which sets throttle position is seeking an idle position and has lost its reference settings.

Attempt to set it: Turn the ignition key ON but do not start the engine. Press the accelerator pedal slowly, all the way to the floor. Repeat this 5 times. Turn the key OFF for one minute.

Start the car. This procedure might correct your problem. If not, you will need a technician with a Cadillac test set to perform a TPS learning procedure.

11-02-08, 11:12 AM
Hey Sub, with those codes, don't you think that the TPS has gone "TU".

11-02-08, 04:03 PM
Yeah, looks that way, but it's too bad because the OP is going to have a heck of a time getting a TPS assembly to The Netherlands.

11-02-08, 04:20 PM
Why is that?

11-02-08, 04:34 PM
.............going back in time to some of my problems finding 327 Chevelle parts in Naples :sneaky:

Does Lindsay or Brasington ship overseas ?? Maybe one of the multi-line mail order houses.

11-02-08, 04:46 PM
rockauto.com does shipping to the Netherlands ...
most of the time ive ordered with them shipping cost was around 60 usd and takes around 5 - 7 days to get to the Netherlands

i think ive still a tps laying around from a STS 1994... if u want, i can try and see if i still go it.

11-02-08, 06:09 PM
.............going back in time to some of my problems finding 327 chevelle parts in naples :sneaky:

does lindsay or brasington ship overseas ?? maybe one of the multi-line mail order houses.

11-03-08, 12:27 PM
Hello Snacky,

I'm gone write this in dutch because thats a bit easier for me.

Erg bedankt voor de reactie op mijn topic. Zowel voor het adres van Arton als over de TPS. Ik heb al het een en ander bij rockauto.com besteld.

Wat betreft de TPS zou ik deze graag van je kopen in de hoop dat dit effect heeft op mijn probleem. Wat zou je prijs zijn en is deze geschikt om te gebruiken op mijn 4.6l northstar van 1993?

Alvast erg bedankt en groeten,


11-03-08, 01:51 PM
PS: You can mail me on: fhogeweg@zeelandnet.nl

Very much tanks for your help !!!

11-03-08, 01:54 PM

ik mail je ff...
Zeelandnet ... Okey.. dan woon je dus in zeeland.. ikke ook! (vrouwnpolder)

12-18-08, 03:54 PM
tang tang wala wala bing bang!