car running rough seems rich

[cmz829]

my 92 mtx is giving me a little trouble. it happened as i was pulling out of the gas station. so i figured it was bad fuel but a month later and a tank and a half later it is still running bad. sometimes it snaps out of it and gets back to normal power. it seems to have really increased the noise level of the car when it runs rough. it idles around 500-600 but has a pulsating rpm needle. if i get on the throttle i can hear the secondaries open but my rpm guage is only reading about 2.7k and it doesnt seem to get above 3.5k even when i know that it is nearing redline. occasionally it just completely runs normal and during that time the rpm gauge reads correct. it sounds like a sensor of some sort to me and ideas?

 

[93rev2sev]

Make sure the intake hose is clamped solidly to the throttle body.

While you are fiddling with it...take a look at the MAF sensor. If you are still having problems after confirming that the intake is installed tightly, unplug the MAF sensor and take it for a spin. If there is marked improvement, you will need to pick up a can of MAF sensor cleaner and a t20 or t25 SECURITY torx bit.

 

[itwonder]

So your tachometer is reading lower than actual RPM? That sounds like the DIS needs checking out, it may either be going bad or have improper grounding. Maybe a failing CPS/CID as a long shot. The DIS generates the signal for the tachometer, and that signal branches off in the wiring harness with one branch going to the tachometer and the other going to the ECM so the computer knows what the RPM is. Of course, the tachometer itself may be failing.

 

[Cal93sho]

Mine had the same stuff happening with RPMs that you are talking about plus engine sounded like a subaru, changed the DIS and now back to normal. Good luck.