Jumpy RPM

[foofers]

When I'm idling I can see my RPM needle jumping around from 800rpms to 1500rpms. The engine doesn't actually rev up and down...its just that the RPM needle twitches - it doesn't happen all the time, just once in a awhile. What reads the RPMs? the CPS? I believe my CPS is leaking some oil, so I'm not sure if that is realated. So if anybody could help me out - thanks.

Also lately the car has problems starting and idling at times- it takes a lot of cranking to get it to start - and sometimes it backfires and I can smell gas. It seems that one of the cylinders isn't firing / getting a spark? So if this is not related to the above I'm guessing I need to change the spark plugs. It's been a year since I last had them changed.

Thanks for the help in advance.

 

[Joel W.]

Any codes present?
http://www.cygnusx1.net/supra/library/TSRM/fi/FI_023.html

 

[hottscennessey]

could be bad alternator.. or at least I had these RPM voltage spikes which I could NOT find the source of them (they would strand my car), finally I replaced my alternator and they went away. When cruising I could see the needle jump and my car would bog due to the ECU dumping fuel. Fix it while you can, dont let it blow your motor because of a dip or spike in RPM voltage.

 

[foofers]

I'll check for error codes tonight when I get home - thx

 

[mrnickleye]

The tach signal and injector pulse are related (tied in together).

 

[foofers]

Haven't had a chance to check the car out...it's actually at the mechanics right now.

Would dirty injectors cause the tach to jump around then?

 

[pimptrizkit]

no but it sounds lik their tring to get you to do an injector cleaning, which isnt' a bad idea on a car this old..

 

[foofers]

Finally after a month of doing nothing....i checked my error codes. I get code 14 and code 21. CODE 21 = Oxygen Sensor which i probably just need to replace. CODE 14 is the ignition system. So from here what should I check? If my CPS wires seem to have been soldered could that cause the error? Also I think the #3 ignition coil might be a little dirty - has some greenish/white crap on it. The spark plugs wires and spark plugs I assume are good because they are new.

Odd thing is when they replaced my spark plugs, for awhile the car felt stronger and was easier to start. Now I have to crank it a few times to get it going...and sometimes I feel that one of the plugs does not initially fire (I can feel the engine shaking a bit) after about 10-30 seconds it smoothes out.

Any input would be appreciated.

 

[suprashy]

Did you calibrate your TPS? I was getting fluctuating rpms whenever I revved her up to 2000 rpms while in neutral. Shifted my TPS over a bit, and fluctuations stopped. And when I had the fluctations, I did not get the famous TPS code. I would double ck. the TPS. (Now my symptoms were not the same as yours, my idle was fine, I would only get this after reving her to 2000, but its worth a shot). HTH and good luck!

SupraShy

 

[jdub]

I had a very similar problem. The tach started jumping up/down then the gauge fuse blew taking out the entire instrument cluster, plus causing all kind of other problems. Turned out it was the harness...it touched the EGR fitting that attached to the intake manifold, melting a small area. It was shorting out the tach signal...I pulled the harness up, removed the cover and taped the melted wires (there were 3). It fixed the problem.

 

[hottscennessey]

I'm telling you man, I used to get code 14 too, I replaced my alternator and it went away. Just swap it out for a day and see what happens. It only takes 15 minutes if you have a supra-bud who will swap with you.