97 Nissan Pickup 2wd A/T Idle issues

[88m5]

Hope you guys can help. So i been trying to chase this problem of High idle (1500 in Park) and then after a few minutes it will go down to 800-900 and stumble for a minute or two and then back up to 1500. So I installed a new IAC valve which made it worst so installed the old one back on. I check the TPS and adjusted it by the NTB99-053b and still the same. I check the EGR and it seems fine. The truck runs like a bat out of hell great other than the idle. I check all the vacuum lines and even sprayed WD40 around the TBI base and intake no vacuum leaks. I also do not get any codes at all.

About a year ago I installed a new MAF which I got from Courtesy Nissan so it original Nissan, Converter, and both Oxygen sensors.

So I am kind of stump here any suggestions would be great.

Thanks

Chris

[Rev_D21]

Sounds like an air leak even if you tried the wd40 trick, which IMO never reveals much. I would hook a vacuum gauge up and see where you are at.

[88m5]

What is good to use for finding a vacuum leak? Carb cleaner or propane? Also is it possible for the EGR valve to not seat all the way close? If so how can I check that? I did use a hand pump and applied vacuum to EGR and truck stalled out, it also held vacuum leading me to believe the EGR is OK.

Thank You

[Rev_D21]

For tracking a vacuum leak I have said this a million times on this site...buy a cheap vacuum gauge and start taking readings. If you have a leak it will show on the gauge as low in.hg. Leave it hooked up where you can read it and take the truck for a drive watching the gauge as you accelerate, cruise and decelerate. Watch the needles value and how the needle moves, is it smooth or does it wiggle, ect. That is the cheapest and most helpful diagnosis tool in any Hardbody owners tool box. Report back your findings and we can start narrowing down your problem.

[88m5]

Ok I have a cheap gauge and will hook it up and give it a drive. I did do this today I decide to do the check of the FIC (Fast Idle Cam)Inspection and Adjustment and it was way off. So I adjusted till the A/T mark was center with the roll pin. Then started truck and warmed up and adjusted the lever roller and top of FIC to 0.83 for Automatic. It now idles down still stumbles after a few minutes. I know i did mess with idel stop screw which your not suppose to mess with. How do I set it back? Should I adjust it to when it just start opening the throttle valve? Also should I do the TPS again.

Thanks

[88m5]

Ok hook up vacuum gauge. When it idles and its good it reads 19 at 1000 rpm when it starts erratic idle it drops down to 15. If I hold to 2500 rpm it reads 20. So took it for drive at 55 mph when it good it reads 20, but when it starts to stumble it goes to 15. The needle seems to move smooth. It feels like when a carburetor is way out of adjustment. It runs great when you are on the gas it just when you try to maintain the speed it is good for a while and then starts to stumble and I can see the vacuum gauge go from 20 down to 13-15. Any ideas?

[88m5]

Well Fixed the Truck today!! I replaced both gaskets where the TBI bolt on to the intake. The gaskets did not look bad since their the metal type gaskets installed new ones and everything seems fine. I had to adjust the idle screw in all the way closed but it idles at 900rpms in Park and in drive it is 700rpms. I wanted to thank you for all your inputs it definitely help me narrow it down. Truck idles and runs great.

Thanks

Chris

[Q451990]

Awesome! I'll have to tell my neighbor that bought my '97 who occasionally mentions having idle problems. Please let us know if the issue comes back and it turns out that this isn't the fix...

Thanks!

Heath

[Rev_D21]

Glad you fixed it! Those vac gauge readings were low and indicating a leak as I thought. A leak at the TB would cause those problems. Glad to hear you and your Hardbody are back on the road!