# 1990 Sentra developed poor idle



## Galimba1 (Aug 16, 2002)

So I'd like to preface, I'm in california, and our draconian clean air bills help us breathe, but increase basic maintenance on our old cars

My 1990 Sentra runs, but just barely. Cold startup is not a problem. However, once it warms up, my little red sentra has poor idle, and acceleration. It actually slowly revs down and dies when warm. When cold, RPMs hold ~1200+ rpm.

Anyone have a vacuum diagram I could follow? I can't seem to locate my FSM at the moment, and I'm working my way through the list of items:
MAF - finally removed, and cleaned with generous amounts of carb cleaner. Had to pull off what I think is the TPS and multiple vacuum hoses
vacuum hoses - I changed quite a few, but not all the hoses. The vacuum lines to the gas carbon canister, to the EGR, and a few others I can't name have been replaced.

Some components I'm still in the dark about what their actual function is. like there are two similar looking components side-by-side, with 2 ports on one end, and a port on the back end. Facing the engine bay, these things are on the left, above the intake, just behind the valve cover. I think they're valves connected to the vacuum system, but I have no idea what they do. 

If you have a PDF of that vacuum diagram (1990 sentra; GA16i), and/or suggestions on fixing idle, please PM me, thanks.


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## Car guy (Mar 31, 2016)

Those are the (combined) EGR/carbon canister solenoid and the (stand-alone) AIV solenoid. The first should only open after warm/hot (140' as I recall) and during cruise, and should close during decel. The latter opens during cold, but then should close. The AIV valve on the driver's side top (next to the valve cover) has a reed valve inside that can get carbon'd and remain stuck open. Have either of these ever been replaced? Has the BPT valve (to the left) of the EGR valve ever been replaced? Is its top circular air filter passing air? 

What's the mileage?

Also, has the ISC valve on the back of the TBI been replaced? Or ever removed and cleaned?

And, has the CTS ever been replaced?

The MAF should not have needed too much cleaning. It self-cleans every time you turn the car OFF.


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## Galimba1 (Aug 16, 2002)

Okay, been a while. . . 
Mileage is 200K plus something something.
I've cleaned the EGR and the IAV, the valves had quite a bit of carbon buildup, but not artery blockage quantities.
I think when I put the MAF back, I may have put the throttle sensor back in not the same spot. . . how sensetive is that position/angle when installing that part?

The BPT valve is still working. The AIV is still working, all valves are still original parts.

I'm not familiar with the ISC valve or the CTS. F.I.C.D. solenoid valve? A.A.C. valve?

After experimenting with the MAF. . . turns out my crappy PVC bolt-on was causing blockage issues on the MAF window on top of the TBI.

I removed said crappy components, and surprise. . . the car idles just fine. One problem I now have, is a solid high idle at ~1000 to 1500 rpm. Shouldn't that be 800-1100 rpm?

Another separate question - the MAF had this white stuff when I unbolted it. Is there supposed to be white silicone grease on the surface between the MAF and the TBI body?


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