Shuddering around 40mph

Kyle Anderson · Post by **Kyle Anderson** » Sun Mar 23, 2008 11:54 pm

This is a problem with the beater, 95 Lumina APV 3.1 auto... the Beretta is also dead, but that's another ball game.

I've had the problem since I bought it, and the guy I got it from even informed me of it. It's finally annoyed me enough to check it out, and I want it running prime when I sell it.

Anyway, as the title says, it's shuddering around 35-45 mph. Kinda like a light missfire at random times. There really doesn't seem to be any real rhyme or reason to it.. I *believe* I can feel lightly it at more or less speed, but I can't tell for sure. One thing I have noticed is that it usually happens right after shifting into the last gear (3rd, 4th... I really don't know) just cruising along. Doesn't happen with my foot off the gas, and not noticable when accelerating.

My first guess was a whacky TPS because it happened only when cruising at that one speed. Jump to two days ago when I finally borrowed a scan tool. I found no variation with the TPS at any position during a road test. The only thing I found out of place was with the o2 sensor readings... they were all over the place. Keeping a steady pace, no matter the speed (including idle), the value (measured in mV.. not sure what it is) varied as much as 600, and it was jumping back and forth between lean and rich. From what I gathered, the range is from 0 to 1000, so something there probably isn't right.

I figured I might as well start with a new o2 sensor. I picked one up, but haven't had a chance to get out and replace it yet. When I was talking with the guy at the parts store, he said a coolant temp sensor could also give the same results... can anyone attest to that?

I'm just hoping it's not a transmission issue, since I'm a complete noob when it comes to anything tranny-related. I'm open to all suggestions... I just want to fix it before I sell this damn thing.

SuzukiGhostRider · Post by **SuzukiGhostRider** » Mon Mar 24, 2008 12:08 am

The guy at the parts house is a moron. I've never,ever heard of a coolant sensor causing shudder or any problems besides not opening the thermostat , causing the fan not to kick on , etc. I hate to state the obvious solution here, but have you checked your tie rod ends or balance on your tires? Both would cause shudder at speeds in excess of 40 mph. It could very well be your O2 not giving proper signals to your ECU for air/fuel mixtures as well. It sounds like your O2 is all over the place so I would definitely replace that. Let us know if it solves the problem and we can work from there. GL.

Kyle Anderson · Post by **Kyle Anderson** » Mon Mar 24, 2008 12:20 am

I know for a fact it's not suspension related. It's hit-or-miss when it happens, and a suspension problem (especially wheel/tire) would be a more regular occurance.

Hopefully I'll have some time to replace it tomorrow... not looking forward to it since it's going to be a pain in the *** to get to. Damn thing is on the rear exhaust manifold tucked way the **** back in the engine bay... just another reason to hate minivans

Kyle Anderson · Post by **Kyle Anderson** » Mon Mar 24, 2008 12:21 am

and yeah... I was kinda thinking the same thing about the parts jockey being an idiot

SuzukiGhostRider · Post by **SuzukiGhostRider** » Mon Mar 24, 2008 12:24 am

LoL! Alright, bro, well fill us in after the O2 is in there. I know you're right , mini-vans suck balls to work on.

Kyle Anderson · Post by **Kyle Anderson** » Mon Mar 24, 2008 12:42 am

I visited my old pal Google to do some more research and came across this:

http://wps.com/LPG/o2sensor.html

Judging by this, it seems my o2 sensor is operating properly... here's just a little snippit:

"You are looking for voltage to go above and below 0.45 volts. If you see less than 0.2 and more than 0.7 volts and the value changes rapidly, you are through, your sensor is good."

If you're up for a little light reading, it's a very informative article.

SuzukiGhostRider · Post by **SuzukiGhostRider** » Mon Mar 24, 2008 12:45 am

Hmmm...but you said your readings were all over pretty bad? If the O2 IS good, then it's starting to sound like a possible tranny problem.....Hope not for your sake.

Mr. Beefy · Post by **Mr. Beefy** » Mon Mar 24, 2008 8:26 am

Could be the ICM or a coil going bad.

Asylum · Post by **Asylum** » Mon Mar 24, 2008 12:31 pm

It is really quite unusual in the overall scheme of things for an ECU to actually go bad.

Check the coils (5.5 ohms tower to tower) and the injectors (2.9 or so as long as they are consistant).

Does it miss at WOT?

WOT bypasses the O2 Sensor.

Kyle Anderson · Post by **Kyle Anderson** » Mon Mar 24, 2008 6:03 pm

It does not miss at WOT.

I'm going to check out the coils and injectors right now... I'll let you know how they check out when I get to a computer again.

speedygtz · Post by **speedygtz** » Mon Mar 24, 2008 7:01 pm

possible egr?

Mr. Beefy · Post by **Mr. Beefy** » Mon Mar 24, 2008 8:37 pm

So did you actually change the O2 sensor?? Like Eric said @ WOT the O2 is bypassed so it wouldnt do it. Might want to check the wiring going to the O2 sensor as well.

Kyle Anderson · Post by **Kyle Anderson** » Tue Mar 25, 2008 9:21 pm

Soo... I discovered today this engine is crazy old-school. This is not the same 3.1 found in l-bodies and the such. This is the first time I've really gotten acquainted with this beast.

First of all, it's throttle body injected. Two injectors up top... popped the wiring off and checked the resistance. I got a consistant reading between the two on multiple tests. I can't say for sure what resistance they are because I was getting different numbers from test to test, but consistant readings between the two injectors on each test. Damn $300 multimeter... fine time for it to screw up

It also doesn't have coil packs; good 'ol distributor here. I guess this presents a new option... maybe replace the cap and rotor?

I have not replaced the oxygen sensor yet. I'm starting to think less and less that it's the problem, and it would be nice to get $20 back if I don't need it.

Mr. Beefy · Post by **Mr. Beefy** » Tue Mar 25, 2008 9:42 pm

It's ALWAYS good to replace your O2 sensor no matter what.

Kyle Anderson · Post by **Kyle Anderson** » Tue Mar 25, 2008 11:03 pm

I might just say screw it... a guy I work with would buy it today if I could find something else to drive, which I might have about an hour ago.

http://nmi.craigslist.org/car/618543774.html

97 Audi A6 Quattro. Only an hour away, needs a head gasket, only a grand... Audi's are sooo damn nice. Base price on these cars was over 34 grand new!

I figure another $500 and I'll have one amazing car. Already e-mailed about it, and hopefully I can get up there soon to check it out. Only thing that sucks is the gas milage and it takes premium.

Anyway... that was off topic

As for the van, I'm going to fix the ABS and get that seatbelt light fixed and call it a day... it's a 13 year old beater; it's not like it's worth much anyway. It's not worth my time and money throwing parts into it chasing a problem I'm not certain of.

If someone can think of other things to check, I'm all ears... I'm not going to throw money into random parts though. This oxygen sensor is going back.

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