alright....had some stuttering kinda fluttering RPMs...not necessarily only at idle.....i went home last weekend and worked on it a little..(i changed a bunch of vaacuum lines that were old and dried, i cleaned the IAC with carb cleaner, and went ahead and changed the O2 sensor.) well, i thought it was fixed (i drove 100 miles back to gainesville, no prob), but tonight, the symptoms return! so WTF? should i look elsewhere for a vaacuum leak?(maybe at manifold? or other lines?) is there anything else i can check????? seriously, i'm about to just take it to a mechanic. (of course, im in gainesville, where i dont really know a good mechanic i can trust)

by the way...its a 91 3.1

 

are you sure the tune up is good? no codes stored? might want to put a vacuum gauge on it and see if you actually have a vacuum leak. might also want to try a compression test.

 

Dude I am in the same boat you are. My damn car is doing the same thing.

 

As Ed hinted, verify that you have good plugs, rotor, and distributor cap. Clean and meter the plug wires. Recheck the vacuum hose routings against your VECI label under the hood. Often overlooked as potential vacuum leaks are the HVAC system, cruise control, PCV system, and power brake booster.

And how are you determining that the RPMs are fluctuating? Is it simply a tachometer indication or can you feel a misfire or surging? If you can feel it, you may have fuel delivery (injector or fuel pressure) issues as well, but it will be easier to track down once the ignition system is inspected and given a clean bill of health.

 

ok...first, yes, i can see the RPMs jump on the tach AND i can actually feel/hear it. i went and looked around a little at the other vacuum lines...they look good but who knows. i have tried the WD 40 test but the problem is that this doesnt happen all the time....seems like when i wanna test it, it is fine...then later, it is back. i do not have a vacuum gauge (or even know how to utilize one)....ignition stuff is sound....should i just give up and take it in??? oh and MOST IMPORTANTLY::is it ok to keep driving like this or will it hurt something worse??? thanks guys!

 

Could very well be an ignition problem! I had the same symptoms once with a corroded cap. The computer would go on the fritz now and agian because the spark to the left cylinder bank was getting a cylinder missfire. So with the 02 reading the left bank it was sensing unburnt air in the exhaust, and adding crazy fuel, thus causing sputtering. It doesn't sound like a vacuum leak. Go over the ingition again, test the spark plug wires too. A small ignition problem would almost always go unoticed in a carb vehicle, but the same problem in a efi vehicle can be a real pain in the ***.

 

I would be willing to bet it's ignition related. I found out I had distributor problems. Also my ignition system is suspect. I am working on the problem though. But when I adjusted my distributor I found that things improved. However my timing is way off. And my timing is fluctuating real bad due to the fact my ignition system has issues. I need to do some wire repair and possibly coil replacement.

 

open up the valve covers and see if there is any crap in there, if there is, clean it out and pour some diesel gasoline in there and run the car for 30 min, then change oil/filter. that should help

 

* i had a real rough idle so i did that and it helped a lot

 

i just took the cap off and looked at it....i think im gonna go ahead and replace it.

oh yeah, PS, B.T.T.T

 

Very similar, but I also can feel the car nearly die while driving (I'll gas it and it 'prevents' any change. Car also dies in park. Happens every once in a while, and sometimes I get a S.E.S. light w/ a code of 15.

Anyway, heres what I have narrowed down what it isnt:

Fuel Filter (thought it might be stumbling)
Vacuum leaks (I recently replaced EGR Valve)
Cleaned IAC


Anyway I can drive for an hour no problems, but when it happens I notice it sometimes smells like fuel and I have trouble starting it and have to wait a half hour or so (that's why I'm guessing fuel issues.)

I will try the test of the fuel pump, maybe it's going bad, but I hope it isn't that P I T F'n A.

Is this a somewhat common thing? for those years (90-92) Cause I got a 90 5.0.

Jm

 

While you're changing the cap (and hopefully the rotor) you might as well meter the plug wires. Don't forget the dielectric grease for the plug wire boots when you reinstall them.

Hopefully, your replacement cap will have brass terminals and deep arc chutes. In other words, don't cheap out on a new cap - get Standard PLUS! or other premium parts.

 

How does a bad or aging coil feel? I removed my hood seal,and the heavy rain allmost completly shut down my spark. Now a few days later I'm getting the fluctuating idle and funny drop in engine power when letting off the gas. I know to check for moisture inside the brand new cap asap, but 190,000 miles could be about it for the coil ???

 

yeah thanks Vader...i was gonna change the rotor and even the wires too.....and perhaps when i go home (im at college...dont have my real tools here) i will change the plugs.

 

JDM...does changing the EGR valve mean you have no vacuum leaks??? mine doesnt really die and i havent got any idiot lights either.

 

Someone told me to check my coil also, no real way to check if its bad other than replacing it,and it's only $13 at advance auto.


Squirrelly:

Changing EGR doesn't mean all leaks are gone. The EGR system does have 4 different connections and a couple of plastic lines that can get brittle. The reason I changed mine is because of a code 34.

To check for leaks you can by some carb cleaner and spray it into every vacuum hose while the car is running and if it dies or dips you've found your leak.

You can also rent a vacuum tester from auto zone for like $30 and get the $30 back when you return it. The tester is good if you find no leaks but want to check for weak flow/blockages.


Jm

 

My car is doing the same thing. I checked fuel output from the fuel filter (fine), changed the coil, disconnected the alternator, and checked vacume lines. I dont know what is going on. Idle is very erratic and rough. But it is not all the time. When it is idleing fine, I will give it some gas and it will start doing it agian, and eventully it will die. It is not giving any codes either. Need ideas!

 

Well I checked my coil and distributor. They were good afterall. I am having a hell of a time tracking this problem down. I may just break down and put it in the shop.

 

I changed my rotor and cap and my problem is now gone. If you are sure they are good, and I mean 100% sure, thats fine, but if you are not 100% sure, I would change them. I didnt think it was my problem, it just didnt have the normal cap and rotor symptoms, but my missing problem is now gone. What I found out was my rotor might have been somewhat lose and may have been rocking foreward and backward, but it did show wear.

 

I believe that my throttle position sensor is at fault. I will know in a week or so when I get paid. The part costs me about $30.00 or so. I'll let you guys know how it turns out.

 

Thats really easy to test, you could buy a cheap multimeter for less than that, and test the parts

 

What is the proceedure for testing that? I have a Haynes manual and it's not worth a damn. I have not found any Chilton manuals for the car either. So any info you have would be appreciated. Thanks.

 

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

Thanks alot I will give that a try.

 

Hey i was looking at that IAC adjustment on that link.....i dont understand the part about the U-shaped paper clip .....what/where is the ALDL, A and B pins??? can someone explain this to me?

 

when you look at the aldl connector, the pins start in the top right, ie: pin a. then pin b is second from the top right.

 

Before you waste money on a tps why not check it first? A defective TPS will generate an erratic voltage when you try to set it. You can also unplug it, and from the center pin to either end use an ohmmeter and check to see if the resistance varies smoothly as you move the throttle. I like an analog meter for that test.

 

but WHERE is the ALDL connector????

 

nevermind about the ALDL...i found it in the archives.

 

Well I have finally gotten around to testing my TPS sensor. I borrowed a multimeter to do it. And as it turns out my sensor was out of spec. I reset it to spec and it still wouldn't put out the correct voltage readings when I opened up the throttle all the way. The voltage was also not consistant just like the article on this site suggested it should be. So it would appear that I have to replace it.

 

ok, time to look at this one again, fellas.....i have as above mentioned:

changed cap and rotor,
replaced a buncha vacuum lines, check valve, checked w/ wd40
checked wires (for arching at night and flexability)
checked TPS with multimeter
changed IAC
checked for trouble codes (none)
reset idle

AND THIS IS THE KILLER....i took it to a shop....they charged me 60 bucks for "diagnostics" to tell me that the "idle speed motor" is bad, and maybe there are other problems, but that is where to start. they would replace it for a grand total of 200 bucks! i said no way, heres your 60, ill do it myself.

27 bucks later, i have a new IAC (that is the same as idle speed motor, right???), so i think im good while driving to reset the ECM, and then!!!! it is so back. so now i feel sooooo screwed! i paid 60 bucks to a lousy shop for nothing. i am calling them tomorrow (they are closed at this time)

but what else could it be????

I NEED HELP URGENTLY!

plugs? wires? MAP sensor? elusive vacuum leak?

i asked if they checked the MAP sensor and if they put a vacuum gauge on it, but the service guy(not mechanic i guess) didnt know.

 

You need to check the wires with an Ohmmeter. If you've got an open wire, the tach will bounce a bit. In fact, my EGR just ate my #3 wire and caused the same thing, bouncy tach.

The wires should have about 3000-4000 ohms per foot. If it reads OL it's junk.

 

hmmm i think im gonna take it back to taht shop tomorrow and make them do it! hell i paid them 60 bucks for ummmm NOTHING! im gonna ask them to check wires(not just visually), check map sensor (is there a way to ),and check coil, module, put a vacuum gauge on it, and check fuel injector resistance.

hows that sound??

if they dont do it, im gonna call the consumer lawyer! ha

 

Look for white marks on the sides of the coil.. If they are there get rid of it..

Injectors will usually cause a problem when you snap the throttle instead of at idle..

Fuel pressure could be too high.. Regulator slammed shut ?

Also how are the spark Plugs ? there not crossfires or platinum or anything like that are they ?

 

A good shop should have an ocilliscope to check the ignition system . Find out if the shop checked the car with a 'scope.

If they don't have a 'scope, just get a $20 DVOM from radioshack or some place and check the wires. Then at least you'll gain a good tool out of it.

 

Would this be a possible reason? I know it says its for late model GM's but ya never know..

Also has anyone ever done the ECM tap test? Supposely you can tap on top of the ECM housing and see if it makes the engine run different or throw codes out.. not sure.

EDIT- Here's a link for the tap test: http://www.bsecorp.com/tech/bdtecb102.pdf


Erratic Warm Idle Late Model General Motors

An erratic, high, or searching idle condition on late model General Motors fuel injected vehicles can sometimes be caused by the presence of AC voltage from a leaking alternator diode on the ECM's DC power lead.

The momentary voltage drop that occurs as the AC voltage crosses the positive/negative voltage threshold appears to fool the computer into thinking that a drop in system voltage has occurred. The ECM reacts by increasing engine RPM and boosting the fuel mixture to compensate for the incorrectly perceived low voltage condition. Technicians can test for this condition by attaching a voltmeter , set to display AC voltage, to the main alternator output terminal. The presence of AC voltage greater than 2 volts would indicate that alternator service may be required.

 

Yes, I'm a driveability tech and have done many tap tests. The tap test is usually done on a pcm in a vehicle that has intermittent problems... Especially die'n out problems.. Whack on the ECM and the car will die. I've also started dead cars by hitting on the computer. You'll be told that it could cause damage to a computer but I've never hurt one.

 

I still think you have dirty spark!

 

I am in the same boat again. I just replaced my TPS sensor. I am still in the same damn position. Oh well. I may just have to put it in the shop.

 

To many variables here. Kinda flutters but not only at idle ? Does that mean it misses under accell sometimes too ?

I'm thinking ignition almost for sure. Plugs, wires , coil ect....

Fuel pressure is probley ok... If the car runs fuel pressure is more of a looses power thing when driving. Unless it's a black smoke issue or a smog failure with high C.O. However...

The Computer System....
Just because no codes are listed doesn't mean there isn't a problem. Alot of sensors can test good when the computer assess there values. You might have a bad O2 sensor and the cars going lean because the O2's telling the PCM your rich when it's not. If your V6 is a speed density system the car might think it's at 10,000 feet and it's at sea level. You might be in the Mohave desert as far as the computer see's and your in Alaska. That's why the ability to read Data is important..
and ...
Is the EGR solinoid letting a small amout of vacume through at times ? The ECM can't tell if the signals says it's shut down.. Well unless you have a O2 temp sensor... Or maybe the EGR is binding causing a small amout of vacume to leak internally.

Lotsa of possibilities and probley alot more....

 

ok, i went back to the shop...talked to a mechanic. he cmae and and looked at it a while with me, real nice and helpful guy.

he says he is pretty confident that it is ignition related. i went out and bought a multimeter tonight, probably wont get a chance to mess with it till saturday, though. guess ill check the wires with it. (DO i put one test lead on each side??? which one where??) i will also pull the plugs and check them out. also will check the pick up coil. can i check the module or the coil??? how??? and is there an easy way to get to the plugs on the passenger side bank???

90formula:: yes it misses under acceleration also. and i believe it is running very rich (smells gassy, horrible gas milage, and backfires)

 

If it was a V-8 I'd say from underneith but a V-6, I thnk it's from the top.... If you can check fuel pressure should be 33-41 port injection. Throttle body probley 12 max I'll look at work just to be sure...

 

I found that mine was the simple Temp Sensor Unit that tells the ECM how hot the engine is. I bought 3, yes THREE, bad ones (two from Advance Auto, one from AutoZone) and couldn't figure it out.

Had a mech. hook it up and he found out it was indeed the sensor that was causing it. It was sending a reading of -32 degrees making the ecm try to shut the engine off to prevent damage. I would have intermintent stutter/stumbles when driving sometimes, trouble starting sometimes, hard starts all the time, all from this damn $8 part.

In the future go to a chain like midas that does everything, they do free estimates. Some of the guys don't know what they are doing but if you see a guy in charge that looks like he knows what he's doing slip him $5 for looking at it. He'll help you out and remember you next time you need a quick diagnostic.

Jm

 

Yes, set the meter to Ohms ( the horseshoe/ Omega symbol) and do 1 wire at a time. Pull the ends off the cap and plug and stick the meter leads in both ends. (When checking resistance, there is no polarity so you can put either lead in either end of the wire and get the same reading)

You should have approx. 3-4K Ohms per foot. If the wire reads in the high thousands, OL, or in the MegaOhm range the wire is junk.


Yeah, grab a swivel socket and a few extensions and thank g0d you don't have an LT1.



Have you put a fuel pressure gauge on it? Does it hold pressure when you shut the engine off? Pull the vacuum line off the fuel pressure regulator and look for the presence of fuel. Also, missing under acceleration is VERY typical of an open plug wire.

 

AAAHAHAHAHAHAHA!!!

WIRES WIRES WIRES!!!!

i bought a multi meter, checked the wires (found a couple bad ones), checked pick up coil, checked coil,...put on some new wires....and omigod, its good to be home! ha i forgot how it felt to put your foot down with confidence!!!

haha the other day, on my way to the part store (with my awful missing), some chump was next to me in his four door honda accord with rice lights and wheels and a spoiler.....he kept revving....i just laughed it up, like he wasnt worth it, but in reality, i laughed because i knew i couldnt rev without stumbling and backfiring...hahah he so would have taken me tat day
!!!! if i see him again......

i pulled a couple plugs too, looked good, one with a little carbon, but im sure that was recent because of my whole ignition problem....i left them in, gonna replace them over winter break.

 

Hehe, good to hear. How many wires were bad? Did they read OL or just high resistance?

 

two were bad......on one, the ohms kept bouncing all over the place...wouldnt stay steady......the other was OL (i guess?) it didn't read any resistance on it. oh well, new set fixed it!

funny thing is, i bought a set when i first started having these problems......but i returned them because i decided i would rather order some accel 8mm instead. ha could have fixed it all that time and money ago!