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Old 05-04-2005, 06:18 PM
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3800 series revving up on it's own

Hey guys, it's not a hot rod question, but hopefully someone here can help me.

My girlfriend has a 1994 Oldsmobile 88 Royale with the 3800 series one, tuned port injection, 135,000 miles on it.

It had a shutter when we bought it (a month ago). By shutter I mean: If I am going 30mph in 3rd gear and I accelerate the whole car starts to shake. It is very similar to what my 4.6L crown victoria did when it was misfiring due to a bad plug wire. A check of the plugs and wires showed that they were old and wore out, and the air filter was dirty. So, I replaced the plugs, wires, and air filter. I get on the road and the shuttering was gone. For one stinking lousy day. Now it comes back randomly. Sometimes I can drive without any stutter, sometimes it stutters all the time. It shutters regardless of whether or not the engine is cold or up to operating temp.

There is another problem that is rearing it's ugly head that has me more worried. Right before I changed the plugs, sometimes when you started it, the engine would rev way up for up to 20-30 seconds before it would settle down to idle. Now it does it if you are just driving along the road too and quite often. I disconnected the cruise control at the vaccum actuator, and that was not the problem.

Any ideas anyone here has would be very appreciated as this car is the only means of transportation for my girlfriend and I don't want it to break down on her!

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Old 05-04-2005, 08:14 PM
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78novaman
2 things that coulkd be wrong

1. You may have a problem with your computer that operates the car, you can pull this out and take it to NAPA andf they will run a check on it. If you pull this out remember to disconnect the battery cables first, both positive and negative.

2. You may have a special board for throttle control, this maybe acting up and getting ready to go out, if you have this board (and sounds like it) it could be causing your problem, Doc Vette would know more about this then me. Usually they are located on the top of the engine under your cover or close by it.

I would either PM Doc or post a thread asking him for information on the throttle control board, I believe he is one of the most knowledgable on this board when it comes to electrical problems, and maybe he will see this thread.

Hope this helps
30dee
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Old 05-04-2005, 08:54 PM
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78novaman,

Do you get any engine codes? Check engine lights?
I have a 96 3.4 and when it has an engine miss-fire it will set a code. Most of the time it is a bad plug wire one of the ones under the intake plenum.

Godd Hunting
Scholman
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Old 05-04-2005, 08:58 PM
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Lets address the stuttering condition first. Does it do this in first or second gear or only in 3rd or 4th? If only in 3rd or 4th under slight acceleration it may be the tcc. You can verify by duplicating the condition and lightly stepping on the brakes to disengage the TCC. If it goes away it may be a lower than optimized TCC lock up speed. This was called fish bite back in 94 and feels similar to having a standard transmission car in too high a gear then trying to accelerate slightly. There was a prom available that raised the tcc lock up speed. Second issue could be a slipping TCC. If so it will probably worsen. Third thing could be a cylinder dropping out. Under TCC lock up and tip in acceleration the combustion cylinder pressures are higher. A slightly leaking valve (was often cylinder #5 exhaust) can cause the miss. Root cause of this was occasionally water in the fuel rail cutting off fuel to the #5 injector.

The revving up condition at start up is most likely IAC (idle air control). There were several different revisions with different spring colors on the IAC. If it had been fine for a period of time the IAC could be sticking and the PCM (powertrain control module) is loosing track of where it is. Or the IAC is starting to go. Checking with a Tech 1 will show what is going on with the IAC counts vs rpm and will direct the diagnostics the right direction.
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Old 05-04-2005, 10:34 PM
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Stutter on a 3.8 = weak coil... It may have either 3 single coils which is the Delco setup or may have the Magnavox which is all 3 coils in a pack setup...? If its the Delco you can isolate which coil is acting up (will show as a weak spark as compared to the others) and just change it or if its the Magnavox setup then you have to change the whole unit...


I agree on the IAC on the other problem they get old and stick and cause crazy idle problems...
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Old 05-05-2005, 08:26 AM
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Bumpstick is right - could be a coil issue. I do remember they were more prone to some issues when really cold. If not the coil it could be as I listed above as I ran into a number of them back in the 90's.
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Old 05-05-2005, 04:25 PM
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Thanks for all the info. No check engine light comes on. The idle air control makes sense.

I don't think it'll matter now anyway. Last night I was driving home in it and I heard a loud bang. The rear mounts for the transaxle fell out and were just hanging loose in the air! Took the steering out too, column not connected to the steering box anymore. AAA to the rescue! I have yet to go look at it but it's probably not good Now I'll HAVE to get the nova up just for transportation.
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Old 05-05-2005, 04:28 PM
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Although you aren't driving it anymore, I think the problem could be in the intake manifold. It's plastic, and the EGR gases burn through it causing all sorts of driveability issues.

tom
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Old 05-05-2005, 08:41 PM
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Actually, I got a good look at it today. It was just the body mounts that rusted out on it. There are just 4 mounts that take the entire force of acceleration, fighting against gravity too. Really bad design, all the weight of the engine & trans pulls on these 4 mounts, add the reactive force from accelerating pulling down; too much for rusted mounts, snapped right out. They just broke from the rust, the bolts were fine. The body where they were bolted is fine, have to call napa tomorrow and see if I can get another set. Nothing bent by the looks of things.
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Old 05-08-2005, 10:38 AM
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Great news! I spent about 10 hours yesterday working on it, and I managed to put it back together. No major damage was done after the car broke in half! It would have been an easy job except I had to take the column out to put the steering back together.


Drove it around the block and......it still has all the same problems. A stutter when it's @ low RPM and it revs up randomly when it's at or near idle.

I have a friend of mine that works in a shop, he went with the coilpack right out of the gate. If you look at the coilpack you can see that it's arranged in pairs of two's. He told me to check the resistance between those 'sets'. If one is off, it's a bad coilpack. All of them checkout, measuring 8kohm each when they are cold and about 9kohm each once it's up to operating temp. After this, he told me to go to a parts store and buy a light pen to check all of the wires. It supposedly pulses when it's near a spark plug wire and you can adjust it so it pulses smoothly. Check all the lines and if one is different then the others, you have a weak or misfiring cylinder, and a bad coil. This is what I plan to do this afternoon.

I don't know where the IAC is to replace it, sounds like a very good possibility. I guess I have to buy one of those haynes manuals that I despise.
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Old 05-15-2005, 08:33 PM
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Spent $15 and got a Haynes manual for it so I would know where all the sensors were on the engine. Started troubleshooting by pulling the plug on the Idle Air Control (IAC) valve. Then it would rev up all right! Wasn't acting the same though, so I plugged it back in and disconnected the Throttle Position Sensor (TPS). Started it up and it idled fine. Plugged it back in and it revved up again. Unplugged it, idled fine. Plugged it back in, wouldn't even start! BINGO! Pulled the TP sensor off the throttle body and measured it with a multimeter. There are three prongs on the connector for it, two of them only measured 300 ohms and didn't adjust, so I figured the sensor was shot. At the parts store I measured a new one and it was 5.5k ohm and then went down to 500 ohms as the throttle is opened, a hell of a difference! $50 later, I now have a car that doesn't rev up, has no stutter, and the cruise control now works! I figure the computer thought the throttle was wide open and was trying to compensate.

I'm making sure I'm not like those other guys who never let you know what fixed the problem!
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Old 12-29-2008, 05:46 PM
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dose it ever do it at a idle? it sound like ti MAF (MASAIRFLOW)
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Old 12-29-2008, 06:22 PM
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Originally Posted by hevy chevy
dose it ever do it at a idle? it sound like ti MAF (MASAIRFLOW)
This thread is from 2005
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