whatawhipur Posted May 14, 2021 Share Posted May 14, 2021 I have a 1990 YJ 2.5l TBI that has had a high idle issue for a while but it has recently got worse. Awhile back, it would start and idle around 1000, then kick up to 1600 about when it reached operating temperature. This was tolerable, but now it pretty much immediately goes to 2000 after start, hot or cold. The idle speed control or idle air control, not sure which is correct, but the little screw that is supposed to keep the throttle plate open a little bit to let more air in on start up isn't even touching the plate, and I'm pretty sure is broken considering it doesn't ever move, so I know that isnt causing it to idle high. I took a look at the throttle position sensor, which looked okay on the surface, but I probed it with a multimeter and it read 4.6 volts in but read 0 volts out. I think the out voltage is supposed to be 17% of the in voltage but even when I opened the throttle all the way, it continues to read zero. Would this mean that my TPS is bad? I'm relatively new to this so any help would be appreciated greatly. Thanks in advance. Quote Link to comment Share on other sites More sharing options...
Administrators Moses Ludel Posted May 14, 2021 Administrators Share Posted May 14, 2021 whatawhipur...Try drilling down at our many discussions on 2.5L idle issues and Jeep TBI troubleshooting in general. This will provide some insight and context about the system and its trouble spots. The ISA motor function and vacuum leaks would be my first considerations. Vacuum leaks can be at the engine, EVAP system or even the power brake booster (check valve, diaphragm, etc.). If the engine runs well aside from the idle speed issue, the TPS would be a lesser concern. TPS switches do fail or deteriorate over time, however. For accurate test methods and voltage readings on the TPS, sensors and the ISA, I rely on the FSM for these models. I strongly suggest that you invest in an FSM, either a used print version or a less expensive and versatile CD copy of the Mopar manual for your model/year Wrangler. Here is the roster of 1987-90 YJ Wrangler 2.5L TBI discussions at this forum. I will gladly pick up the conversation after you have ruled out troubles addressed at these topics: https://forums.4wdmechanix.com/search/?q=2.5L&quick=1 Moses Quote Link to comment Share on other sites More sharing options...
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