Fluctuating Tach = CID Failure???

[ViPER1313]

My 92' has developed an occasional issue where the tach will seem to "stall" and drop momentarily while revving, then regain it's normal reading. The car never stutters while this happens, and there are no codes and no CE light. The tach never goes to 0, just seems to lose sync by about 1000rpm with the engine (I was accelerating while the tach was dropping.) Also, the car is hard to start on occasion (75% of time catches in 2-3 revolutions, but sometimes will go 10 or more) - the tach always reads while this occurs and the engine does not buck or seem rough when it does catch (new starter + battery BTW). The hard start has occurred for the past 6 months but the tach issue started this week. I'm guessing the CID is on the way out but want a second opinion. Anything else I should check first?? Thanks.

 

[projectSHO89]

Does not sound like a CID fault. The CID will usually cause bucking when it starts to flake out.

My guess is that it is something specific to the IDM/TACH signal (possibly the DIS), the tach, or the interconnecting wiring.

You should have an underhood TACH connection point. Perhaps you can get an external tach connected to see if it mirrors your in-dash unit.

Steve

 

[autobahnsho]

I understood that the tach signal comes straight off the computer. The computer figures it via the CID and CKS (Crankshaft sensor).

Have you checked the codes?

Good luck!

 

[ViPER1313]

I understood that the tach signal comes straight off the computer. The computer figures it via the CID and CKS (Crankshaft sensor).

Have you checked the codes?

Good luck!

Checked them today -

Key On Engine Off - 219 ( engine doesn't seem to bog, never remember seeing the CEL - cleaned contacts for SPOUT circuit today & will clear computer and check again in a few days) and code 542 (no biggie)

Key On Engine Running - 111, also ran Cyl Balance, got 9, so alls good there.

Edit: After further reading the 219 code without the 213 code indicates that the problem has already been corrected - still want to clear memory and see if it comes back at a later point.