Seville SLS '97; After some driving accelerating on its own & high idle

[Arbi]

Hi everybody,

Short introduction: my name is Otto, 26 yo from The Netherlands and since two months the proud owner of a Seville SLS from 1997. Lived in the States a couple of years and always had a thing for American cars. Promised myself my first car would be an American. Kept my promise .

The good people at cadillacforums already helped me out a lot but I still have a problem I'm hoping one of you guys can help me with or relate to.

http://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/659810-sls-1997-couple-questions.html

The problem is that when I start the car it's idles normal and it reacts normal. So I drive for a bit and on the highway. Eventually the rpm will get higher and it will accelerate on its own. This happens at speeds from 0 to 50 mph (rough estimate). On the highway it won't accelerate on its own but it won't brake on the engine as much as it's supposed to do either. I get off the highway and have to stop for a red light. I will have to brake more than when the problem is not happening. And when I release the brake it takes off harder than it's supposed to. When I get home and I want to park the car the rpm in D is around 1000 rpm and when I put it in N or P the rpm is around 1600 rpm.

The funny part is that when I turn the engine off and immediately back on the rpm will be high for 5-10 sec. and then drop to normal. But when I drive around for a bit the high idle and self-acceleration starts again.

So the problem doesn't start right after starting the engine, but only after driving for a while. That's what makes it strange to me.

Note: when I take my foot off the gas pedal and it accelerates you can hear a difference between this and giving throttle. The engine doesn't "rev up" like when I would give throttle. Also when I have it on cruise control when I'm driving at slow speeds (for instance 30 mph.) I'll see that the rpm go up and down, up and down. It's giving throttle and letting go.

Here are the codes I got after a drive a week ago:

PCM P0101 (current) - Mass Air Flow (MAF) Circuit Range/Performance Problem

PCM P0121 (history) - Throttle Position Sensor/Switch A Circuit Range/Performance Problem
PCM P0155 (current) - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
PCM P0603 (history) - Internal Control Module Keep Alive Memory (KAM) Error
PCM P1350 (current) - Ignition Contol System (http://engine-codes.com/p1350_cadillac.html)

At one point when the car had the problem I turned it off and immediately back on to see if it made a difference. Right after that start and the rpm dropped back I pulled the codes again. I think it's these:

PCM P0101 (history) - Mass Air Flow (MAF) Circuit Range/Performance Problem

PCM P0121 (history) - Throttle Position Sensor/Switch A Circuit Range/Performance Problem

PCM P0300 (current) - Random/Multiple Cylinder Misfire Detected

What I've done so far:

- Cleaned TB

- Cleaned IAC valve

- Cleaned MAF sensor

- Replaced battery (it died and made the car start really bad)

I've never worked on cars before and so I did the cleaning with help from youtube and cadillacforums (of course I bought the special stuff: TB cleaner and MAF sensor cleaner). So keep in mind that I can't really tell if a part is good or bad just by cleaning/holding it.

Before I did all this these were the codes:

PCM P0101 (current) - Mass Air Flow (MAF) Circuit Range/Performance Problem
PCM P0108 (history) - Manifold Absolute Pressure/Barometric Pressure Circuit High Input
PCM P0121 (history) - Throttle Position Sensor/Switch A Circuit Range/Performance Problem
PCM P0151 (history) - Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)
PCM P0155 (current) - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
PCM P0300 (current) - Random/Multiple Cylinder Misfire Detected
PCM P0507 (history) - Idle Air Control (IAC) System RPM Higher Than Expected
PCM P0603 (history) - Internal Control Module Keep Alive Memory (KAM) Error
PCM P1106 (history) - MAP sensor circuit intermittent high voltage
PCM P1350 (history) - Ignition Contol System (http://engine-codes.com/p1350_cadillac.html)
PCM P1520 (history) - Transmission Range Switch Circuit (http://caddyinfo.ipbhost.com/index.php?showtopic=12932)
PCM P1599 (history) - Engine Stall or near Stall Detected

What I still have to do:

- Check for vacuum leaks

- Clean/Check pressure valve relief

- Add good cleaners to a full tank of gas

- After adding the cleaners do a couple of good WOT's (think the previous owners babied it)

- Clean the EGR valve

- Clean the throttle cable

- My EVAP system is disconnected, connect it back and see what happens

- Disconnect cruise control

Any help would be highly appreciated!

Thanks guys!

[airmike]

i would start by looking for vacuum leaks. In case you don't know how, start the car then start spraying carburetor/throttle body, mass air flow, flammable brake cleaner etc..at any hoses or connections for intake and listen for the engine to speed up. if it speeds up a leak is present where spraying.

[KHE]

Another way to find vacuum leaks is to have the engine off, remove the main vacuum line at the brake booster and then blow smoke from a cigar into the hose and then look for the smoke that will be present where the vacuum leak is located.

[cdgrinci]

Another way to find vacuum leaks is to have the engine off, remove the main vacuum line at the brake booster and then blow smoke from a cigar into the hose and then look for the smoke that will be present where the vacuum leak is located.

Now that's thinking outside of the box (at least to me; so simple, but so intuitive). Great tip.

[Logan]

I don't have one...but they do make smoke machines to help detect hard-to-find EVAP leaks. Also useful on intake leaks etc.

Not my picture...but you can see the leak on this intake gasket.

I've always just used carb or brake cleaner. But that will not find all the leaks....and won't work for pin hole EVAP leaks.

[airmike]

Great pic Logan. I wish I had one of those smoke machines, but it is kinda high priced for a guy that just fixes his own stuff, and would hardly ever use it.

[Arbi]

Hey guys,

Thanks for replying! The thing with a vacuum leak is that it would occur with a hot and cold engine. Mine has a turnover point where it suddenly starts happening. So I took a look at my codes and it made me think that the P0155 code could possibly be it.

My theory is: the o2 sensor starts working when it reaches closed loop. Til that point (so in open loop) the computer has set values for warming up the engine which means for fuel etc. When the engine is warm and at a certain point goes to closed loop the o2 sensor takes over and adjusts the air-fuel ratio. If the o2 sensor is bad (in my case the heater) it will never go to closed loop and will continue to give it more fuel. Hence my sudden higher rpm and "self-acceleration".

I'm wondering if I change the o2 sensor should I change all o2 sensor, both before the cat or only the bad one? And if I change the bad o2 sensor and it turns out it actually was the source of my problem will the other DTC codes go away as well? Could the MAF sensor be reacting to a bad o2 sensor?

Thanks again for your input guys!

[airmike]

A high idle is often the result of a vacuum leak, which is why I would check that first. Even if your o2 sensors were bad, if you have a leak you will never know you replaced a bad one. If they are not bad you are just guessing and throwing away money.