Trouble Starting, Uncontrolled High Revving

[TheWhiteBrick]

Hi everyone,
I am having a problem with my '94 850T, I first noticed this problem periodically after starting up, but it was not obvious enough to warrant any concern. Upon start-up, in park, the engine would rev up to about 3.5-4k rpms, then after a minute or less, would return to regular idle.
The real problem occurred a couple days ago, when, while pulling in to a parking lot, in drive, the engine would rev up by itself, causing the car to lurch forward. I put the car in neutral to coast in to the nearest parking space, and the engine revved up uncontrollably to the mentioned rpms, with no response from the gas pedal, except to rev it up higher, after which it would return to its original point of very high revving. I turned the car off, and couldn't restart it. By the time a tow truck arrived, he mentioned Volvos sometimes have this high revving problem, and was able to start it so I could take it to a mechanic who was no help at all.
I was able to start it at the mechanics and drive home, but the high revving problem persists, as well as the inability to start the car immediately, it seems to need a cool-down period.

Codes I pulled from the engine are:
443- TWC Efficiency
435- Front H02S Slow Response
414- Boost Pressure Reg
123- Engine Coolant Temp. Signal

Based on what I could research, the problem could be a TPS, 02S, air leak, something turbo related, I'm just not sure. Nothing I read seems to encompass all the errors and symptoms I'm having, unless its just two problems rolled in to one.

Any help getting me in the right direction would be greatly appreciated! I'm tired of being charged too much labor and twice the price for parts!

As a little back-story that may be relevant, the car sat for about 5 years before I drove it. It was a challenge to get running smoothly again, but a tune-up and new Cat got it running and passing smog. The only other work I've had done on it was a new fuel pump and relay.

THANKS!!!

[TheWhiteBrick]

Shameless self-bump for my poor Volvo!
Nobody has any ideas or suggestions?

Thanks!

[precopster]

Hi welcome to MVS!!
In your post you didn't mention if you've checked the most obvious things such as throttle linkage assembly and throttle plate operation. A good lubicant or high temp grease at all the pivot points would be a good place to start.
When the revs go high and you touch the pedal does it feel limp or spring loaded as it usually does?
The answer to this question should point you in the right direction. If the throttle feels normal I would be changing the TPS as a matter of course. They are not terribly expensive but you need to buy a Bosch unit for reliability. Check with Volvo Wholesale Parts (site sponsor)
If throttle is limp.I would be lpoking very closely at ALLthrottle linkage points for wear or rust including the pivot points all the way back to the accelerator pedal.
Post back with your findings and hopefully this will get us closer to your mysterious problem.

[PCars]

I too have an 850 turbo with a high idle problem. The issue is very similar to yours and is probably caused a similar failing component. During startup (seems like every one takes a little too long) it will crank then suddenly jolt into running but the rpms go up the 2000 range. After about 5 seconds it will slowly start to calm down and come down for about 10 seconds resting at an idle of around 950. I don't have a scan gauge II yet so thats just what the tachometer says. Occasionally it will start and shoot up to 3-4k and then stay there! I put it in gear at this point with the brakes on to bring it down. It is starting to get hot here and it seems to be getting more and more out of control.

Here'd what I've tried.
-I started using synthetic motor oil, no change.
-About a month ago I removed the IAC valve and cleaned it out. I also took off the TPS sensor and checked its Ohm readings. No breaks.
When I reinstalled all of these, I started it and it ran terribly for about thirty seconds before calming down. The CEL was illuminated. I thought "great, what did I do?" I made plans to get a scan gauge and check the codes but 6 days later the CEL went off.
-I haven't checked compression on the cylinders in a long time.
-I flushed out the coolant and replaced the Thermostat with OEM.
-I removed the coolant temp sensor and checked its ohm readings in cold and hot water, looks okay.

I would love to get a look at all these readings in real(ish) time but I just can't afford a Scanguage right now. Does anyone have any documentation about how motronic reads inputs, or the logic involved with the outputs. Why would it allow a cold engine to idle so high just after startup? What is it thinking?

White brick, how many miles are on yours? I have about 190k on mine. Let's continue to work on this and collaborate on any improvements. I am about to go out there and try a junkyard IAC valve to see if there is any change what so ever. Ill keep you posted.

-Pcars

[Rocky]

The coolant temp sensor was the one thing that I suspected with your description.
Also wondering if you may have a fuel injector problem. Either leaking or blocked. Tempted to suggest a good dose of techron. Check your plugs to. Any great variation in condition?

[TheWhiteBrick]

Thanks for the responses everyone! I am getting back in to town in a couple of days, and was beginning to think I was on my own with a plan of action.
ALSO---- I can't believe I didn't mention this, and I don't know if it's related, but upon popping the hood, I could see some oil pooled up on the the top of the engine, in the metal waffle-like shapes. (I don't have the plastic engine cover on.) However, I couldn't see any places where it might have come from, possibly a little bit of leakage from the cap? Also, the engine running produced smoke out of the tailpipe as it ran poorly and at its high RPMs. Maybe that will give someone a hint? The oil levels where fine, and its about due for an oil change, but not insanely past-due or anything.

Hi welcome to MVS!! In your post you didn't mention if you've checked the most obvious things such as throttle linkage assembly and throttle plate operation. A good lubicant or high temp grease at all the pivot points would be a good place to start.

Thanks! I didn't think to mention this, but the throttle feels completely normal, and pulling the throttle linkage under the hood doesn't seem to indicate any malfunctions, it engages and returns fine, the cable seems to be moving normally.
I don't know anything about the TPS, but judging by what I've read its something I would attempt myself, I guess I should find/get a voltometer and start checking things out...

White brick, how many miles are on yours?

Right around the same as yours.. my odometer broke a while back (on my to-do list after reading a wonderful write up on here) so I can't say for sure, right now its broken on ~160k. I will definitely be keeping everyone updated on what I am able to test out, I only have some basic mechanical knowledge, so with the help of this site, it will be a lot of learning as I go.

The coolant temp sensor was the one thing that I suspected with your description. Also wondering if you may have a fuel injector problem. Either leaking or blocked. Tempted to suggest a good dose of techron. Check your plugs to. Any great variation in condition?

Coolant temp sensor is another possible lead that has come up in my readings, I will have to do some tests I guess to start narrowing down my search. As far as an injector, that may be a little out of my range of abilitly, so I hope it isn't! Getting some techron in it is an easy try though. Trying to let it run through the problem produced some smoke from the engine from roughly the turbo area, so I ended up shutting it off.

Thank you everyone for reading my long-winded posts, and for helping me out. This high-revving problem seems to occur somewhat frequently, so hopefully with enough of us together, we can help solve it for everyone.

[jblackburn]

I would also blame the coolant temperature sensor.

ALSO---- I can't believe I didn't mention this, and I don't know if it's related, but upon popping the hood, I could see some oil pooled up on the the top of the engine, in the metal waffle-like shapes. (I don't have the plastic engine cover on.) However, I couldn't see any places where it might have come from, possibly a little bit of leakage from the cap? Also, the engine running produced smoke out of the tailpipe as it ran poorly and at its high RPMs. Maybe that will give someone a hint? The oil levels where fine, and its about due for an oil change, but not insanely past-due or anything.

Have you ever cleaned/replaced the PCV system? Smoke from the tailpipe and oil up top sounds like you are due for it, if not.

https://www.matthewsvolvosite.com/forums ... =1&t=28487

[TheWhiteBrick]

So, I am finally home, and I think I am making some progress.
After some pumping and some repeated tries, I got the car to start on its own. The idle was terrible, and it barely kept running, however, it leveled off to a very choppy idle, and would stay running after a minute or so. Smoke comes out of the tailpipe, and upon popping the hood, more oil. After pulling the dipstick later, smoke was coming from the tube, so I am definitely due for a PCV repair/clean, thank you jblackburn for the heads up and the awesome write up! Would this affect the way the car runs/starts also? I am planning on repairing the PCV as soon as possible, but is it driveable enough to get me to work?

Further, after disconnecting the TPS, the car's idle changed, seemingly for the worse, but then I replaced the sensor, and the high idle returned. I removed the sensor again, and this time, the idle returned to normal, and I was able to rev the engine without it saying in it's high RPM's, it would return to idle like normal. After replacing the sensor, it seemed much better, but would take its time returning to idle. It now starts fine, and revs almost fine with the sensor in, but revs normally with the sensor out. Is this indicative of a malfunctioning TPS? I would think so, but I haven't gotten a voltometer in there to find exactly.
Thanks guys!

[jblackburn]

Would this affect the way the car runs/starts also? I am planning on repairing the PCV as soon as possible, but is it driveable enough to get me to work?

Probably not, but a good thing to get on as soon as possible. There (may) be a severe vacuum leak from one of the lines in the system that could cause weird idle issues, but yours sounds like it's something else.

I think you're on to something with the throttle position sensor. Try cleaning the connections to the sensor and idle control valve and see if you can improve matters anymore. If it still acts funky, I'd go for a replacement sensor.

[TheWhiteBrick]

Did I mention I would be learning as I go?
Embarrassing as it is, I may now be on the right track. I picked up my new TPS, took it out of the box, looked at it puzzled, then realized I had not been unplugging and re-plugging the TPS, it was some other connection near the throttle assembly connected to a silver cylinder. The guy at the parts store specifically said this part was not returnable, so I just installed the new one anyway. Chalked it up to a lesson learned, maybe some preventative maintenance, and an excuse to pick up some much needed tools.
However, I did get at the ECS, (yes the right one this time..) and upon attempting to unplug it, it was totally stuck. After finally prying it apart, I found out I had actually disconnected both sides of the plug, but internally the connectors had come out of the plastic plug casing, and were corroded together still. I got them unconnected, cleaned them up, and reassembled the plug. This seems to have had a positive effect on my problem. While at the store I picked up some synthetic oil, and Sea Foam, so I treated the oil and gas with the Sea Foam, drove it for a bit, then did an oil change. Now I am going to clear the codes from the engine, then see how it goes, if I continue getting problems, maybe I'll do a more thorough investigation of the ECS before buying parts this time. Hopefully, the sea foam can help my pcv problem as well.
Thanks everyone for the input, I'll keep you guys posted on how its going in the next couple of days. For now.. its time for a beer.