[88baron]

Hey all. Wondering if anyone can help? I've got a 1988 Lebaron convertable, 2.5, TBI. Almost everytime I start it, cold or hot, it races anywhere from 2-3500 rpm for 5-10 seconds. Then it gradually drops to idle. I have cleaned and rebuilt the throttle body paying particular attention to the AIS. I have replaced the fuel pressure regulator, fuel injector, MAP sensor, throttle position sensor, coolant temp sensor, O2 sensor and updated the speed distance sensor. I also pulled and cleaned the EGR valve and checked for vacuum leaks. I pulled the codes after all this and 23 and 52 came up. The racing on starts is one of the reasons why I did all this work in the first place. Also sometimes while driving [before I did all of this work] if I just touched the throttle it would run at 30+ mph. If I put it in neutral, the rpm would be at 3000+. That is fixed now!,, but the racing on hot or cold start is still there. I'm thinking it's the throttle body temp sensor. I can't find anyone that sells it. The car just turned 100K and is a garaged Florida car with no rust. I've owned it since 1990. I was a master tech [early 1980's] foreman and service mgr for Chev. dealer so I have a mechanical backround. If anyone can help or let me know where I can get a throttle body temp sensor I would really appreciate it. Thanks in advance!

 

[ImperialCrown]

Welcome to Allpar. If the RPM's do eventually drop down, my guess would be a faulty AIS, AIS circuit or AIS drivers in the logic/power module.
The DRB II or III scan tool can report the 'target RPM and the AIS steps' open and the 'actual RPM and AIS steps' open. The DRB II or III can also drive the AIS open or closed to see if it is able to comply with commands. It is a 4-wire device. 2 to drive the motor open or closed and 2 for 'step' feedback to the module.
Diagnose this first before replacing parts. It may not set a fault code.

 

[Bob Lincoln]

Welcome to Allpar!

Code 23 is for the throttle body temp sensor. Code 52 is for the oxygen sensor. Neither of these will affect a cold start. So I would not suspect either one. Several things to check:

1. Examine ALL vacuum lines and rigid tubing very carefully for cracks and leaks.
2. Make sure you used the thick throttle body base gasket to the manifold (3/8"), and not the paper-thin gasket that some rebuild kits have. The symptoms you have suggest a vacuum leak, and a thin gasket can cause that.
3. Make sure the throttle body is bolted down to the proper torque spec. If it's just a little bit loose, you'll get this behavior.
4. Check all engine grounds - from battery to left fenderwell, from battery to block, from the harness behind the valve cover to the driver's rear corner of the block (ring lug) and the braided strap from firewall to the intake manifold.

 

[88baron]

No leaks or cracks Bob. I visually checked & then [carb clean] sprayed them all while idling with no change in RPM. I purchased and installed the larger base gasket, torqued to specs, removed, checked and cleaned all grounds as well as power logic & terminal conections. Car was never exposed to sea spray or northern road salt. Absolutly no corrosion. Everything you suggested I've already done before the post.
Thanks ImperialCrown but I don't have a DRB scanner. A faulty AIS was a thought until the fault code for the TB temp sensor appeared. I don't think a faulty AIS would cause a rich reading for the O2 sensor would it? I'll try to get someone with a scanner. The symptom occures hot or cold, I'd say on 60% of the starts. The other 40% it starts perfect! Thanks for the help!

 

[Bob Lincoln]

Did you use a new O-ring, or make sure the original one was OK, when you re-installed the AIS? And for the TPS also?

 

[88baron]

Everything was replaced. All O-rings & gaskets and all torqued to specs. I followed your instructions on allpar Bob. They were right on! Thanks! Something I did, might have been replacing the MAP sensor, fixed the problem of high RPM while driving. High start rpm was the reason I rebuilt the TB. I replaced the injector because I thought it might have been bleeding after shut down. Replacing the pressure regulator was suggested on another blog I read.

 

[88baron]

I just picked up an AIS motor and TB temp sensor from the bone yard. I'll try them separately and update the post when I can. Thanks for your imput, brainstorming my car issue!