my 89 idles at 250ish. went through a lot of tries to fix it. improved grounds and adjusted the tps(cruiser54). got a brand new tps but problem stays the same. if i get it fixed it just stays for a while but always comes back down. there is one thing that makes me wonder: if i pull the rear vac line of thr manifold the idle bumps up to 750-1000 rpm. is the iac bad? i swapped in a iac of a 95 that i had layin around. fixed it for a short while ,next time i started the jeep idle was back to 250...perhaps map sensor? any ideas appreciated

 

I'b be suspicious of the IAC. Have you ever thoroughly cleaned the throttle body?

 

i cleaned the tb around 2000 miles ago. looked quite clean, anyhow itook it out today and cleaned everything again. it didnt help. after i start the idle is on a 1000rpm drops down to 750 and after half a minute it drops to 250rpm. perhaps i should just get a new iac. both ones (89 and one of a 95 2.5l) have a lot of miles on them. is there a special brand i should get? or is there a trick to test them?

 

Years back after I lost my fast idle at start up I cleaned both the t/b and IAC. I tested the IAC and found it still in spec. Still it didn't last very long. I've been running a Standard Motor Products one since then with no problems. They can be had at Rock Auto.

 

thanks, i will try with the smp one. and see if it will fix it. went for a longer drive today and with a warm engine the idle was around 750 and steady. still low on startup though.