Tach near 0 at idle, Maft Gen II shows 850-900 Warmup. Where to look?

[Andr3w]

I have no idea where to start checking on this one. After installing the engine, I have been having a low idle problem. Before it would say idle was around 500. After a week of the car starting, the gauge now indicates basically at 0. I decided to look at my maft gen II this time and it shows idle at 850-900 and bumps to 1000-1100 when I kick on the AC. When I rev the car the gauge will show 1000 and the maft gen II will show approx 4000 rpm.

Does anyone have any suggestions where to start looking? Idle seems to be pretty stable now after I fixed some big exhaust leaks.

Not sure if the CAS has anything to do with it, but I have converted down to a 1G CAS which is required for the proefi 128. The condition of the CAS is unknown and I have been skeptical about it's condition since the beginning, but seems to be working since I was able to set the base timing.

Thanks,
Andrew

[Andr3w]

Did a little searching and found a thread about the lubricant drying up on the rpm gauge causing more than normal resistance. Thinking this may be the problem since the car has no other issues. Does anyone know what type of lubricant I would need to use? Is there any precautions I need to take when taking apart the rpm gauge?

Hmm also just read that the MSD coils could be causing the issue by having a lot of noise in the circuit. Not sure if that would allow to show the correct RPM. Any thoughts?

[Andr3w]

Checked PTU and looks to be good. Parts store had a replacement so I decided to give that a try. Turned out to be shit. Idle was terrible, tach spazzed out. Put the old one back in and everything back to normal other than the tach being a bit low.

[Andr3w]

Disconnected ECS to see if that would do anything. No luck. Also found out that the active exhaust is opening at the correct RPM according to the Maft Gen II RPM signal. I guess I will have to open up the main cluster

[J. Fast]

Did you check the ETAC module behind the steering wheel under the dash? Mine went on the fritz with non resistor spark plugs. My tach and center cluster gauges started doing their own thing. I ended up having to replace the module.

[Andr3w]

Interesting. I will look into this as I do have nonresistor spark plugs as well. If I can't narrow down the issue, I think I will just wait till after the pro efi is installed and tuned to see if the problem still exists.

[J. Fast]

I believe the cam/crank sensor has a tie in there too. I have buddy who crushed a wire when dropping his engine back in and the tach started jumping around from that issue also. Do you have an oscilliscope?

[UTRacerX9]

I think I'd just press the gas and hold the rpm steady at around 2k as seen on the MAFT, pull off the needle for your tach, and put it back on at 2k and see if that is any better before messing around with anything else.

[Andr3w]

Yes I have an O-scope. I will confirm the signals hopefully this weekend. Should be a good referesher for my bmet certification as well since its been a while since I last touched one. I was thinking about pulling the needle and resetting, but I don't think the rpm's stay consistant. I will double check this as well.

[GTOJOE]

This happened to me when I was building a custom cluster for another user. My laptop showed the correct revs and so did my old cluster. Swapped out the Tach assembly from another cluster and all good again. I suspect that's your issue. If the maft is getting the correct signal then most likely all other devices are working fine. You could first try removing the cluster and pulling the tach out. Clean the connections and try again. I suspect the one I was working on had got some moisture inside and caused the issue.

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