Tachometer fluttering

[satyr2k2]

I've never quite seen this before but, my tach is fluttering. What I mean is, it pulses up and down independently of what the engine is doing. My car revs perfectly and in accordance with what I'm doing with the pedals but the tachometer is going wonky on me. At first I thought it was only doing it when it was cold but it seems that it does it at odd intervals. Could this be a loose connection? Is this something I can fix myself?

[bassplayaz06]

first thing to try is clean the mass air flow sensor. its on the intake box held on by 2 screws. there's a wire looking thing hanging down. get some electronic contact cleaner and spray that a bit then wipe up the excess with a Q-tip. worked great for me.

[satyr2k2]

Quote, originally posted by bassplayaz06 »first thing to try is clean the mass air flow sensor. its on the intake box held on by 2 screws. there's a wire looking thing hanging down. get some electronic contact cleaner and spray that a bit then wipe up the excess with a Q-tip. worked great for me.Did you have a similar issue with the tach? Did this solve it?

[bassplayaz06]

the problem i had was at times it would idle at 1100 when warm when its supposed to be at 800. it doing that doesn't fix it, then the throttle body just past the air intake needs to be cleaned. my 2001 GMC Yukon was idling between 600 and 700 when at a stoplight. cleaning that fixed it. carb and throttle body cleaner is what i used.

[bassplayaz06]

also i just re-read your post, i didnt notice that you said it was independant. but try that. it cant hurt it if that's not it.

[joatmon]

describe "fluttering". How much does the needle move, is it a 100 RPM range or 4000 rpm? how fast does it flutter, once a second, four times per second, once every two or three seconds, so fast the needle is just a blur?Is this still in your 06 GT?

[ehoff121]

Quote, originally posted by bassplayaz06 »first thing to try is clean the mass air flow sensor. its on the intake box held on by 2 screws. there's a wire looking thing hanging down. get some electronic contact cleaner and spray that a bit then wipe up the excess with a Q-tip.Disconnecting the negative terminal battery cable is a pre-requisite. I would not recommend using a Q-tip; when you use MAF cleaner spray (available at your local auto parts store), you let it air dry. See this tutorial on how to clean the MAF sensor. http://forums.genvibe.com/zerothread?id=36907

[bassplayaz06]

i used contact spray and used the Q-tip to clean around it. i didnt use it on the filiment. and it works just fine.

[satyr2k2]

Quote, originally posted by joatmon »describe "fluttering". How much does the needle move, is it a 100 RPM range or 4000 rpm? how fast does it flutter, once a second, four times per second, once every two or three seconds, so fast the needle is just a blur?Is this still in your 06 GT?To answer your question, just today I was driving in third gear, going about 30mph. The tach normally should read between 2-3k RPM. Instead, mine was jumping between 3 and 5. It was oscillating at about 3x per second. This is about as fast as it ever goes.It tends to bounce between very high numbers before settling back, however, I have also seen it just jump a few hundred. Yes this is still my 06 GT.

[joatmon]

not sure where to tell you to look. I don' tthink it's possible for the combined mass of the affected engine parts to change RPMs by a couple thousand RPMs several times per second, so it seems like it's got to be an electrical issue. Looks like the circuit is that the computer reads the crankshaft and camshaft position sensors and generates a tach signal to the intrument cluster. If you haven't had any performance problems, such as loss of power or fuel economy, or any check engine lights, then it seems more likely that the computer is getting good data, and maybe it's just a display issue with the gauge, but it would be worth checking those sensors to see that the electrical connections are clean, secure, and that the sensors are not loose.Here's a pic showing the location of the two sensors:If you had a scangauge or other similar tool that conencts up to the OBD-II diagnistics port, you shoul dbe able to get a readout of what the computer thinks the RPMs are. I'm not sure how fast those things update, or if they would be able to show a change of several times per second.I can think of things to check if you had an oscilloscope, but I don't have one, you likely don't either.and the standard question, was there anything done to the car just before the problem started showing up?

Attached files

[satyr2k2]

To answer the previous question, no- nothing was done to the car immediately previous to this showing up. According to a GM tech over the phone- he thinks it's more likely a faulty instrument cluster. This an enormous expense if I go that route- is there any other fix anybody knows about?This is still an on-going problem. The tach pretty much bounces up and down all the time now.

[satyr2k2]

:::SOLUTION:::The solution was finally found to this issue. The 2006 Vibe GT that I own had an outstanding recall for the PCM (Powertain Control Module). Not only did this recall fix some hesitation (that I didn't know existed until it was gone), it also fixed the tachometer hopping around. This need be documented somewhere!