Idle drops below 500 rpms when I let of throttle.

[dmj]

Every time If I am at a stop if I hit the gas the car almost stalls when I get of the gas it happens 90% of the time if I have the AC on and about 10% of the time with the ac off. I just replaced the Iac motor but the problem continues .Now I have an intermittent Idle surge and The car sometimes stalls on hot starts. I need help.

 

[SouthCaliVR4]

Have you set the base idle?

 

[Terry Posten]

Have you performed a boost leak test?

Look really close at the throttle body shaft seals. And make sure the throttle closed switch is adjusted properly.

 

[mitsuturbo]

You're not running a maf and venting bov to atmosphere, are you?
I know it sounds like a rookie mistake, but i have to ask. People -still- make that mistake.

 

[dmj]

Boost leak checks ok car holds 20 psi up to redline no spikes Timing checked ,and biss adjusted 850rpm @idle. Throttle body was recently rebuilt problems started approx 3 days later after rebuild. Tps set at 10.1% Keep bringing the ideas. I will try every logical suggestion

 

[toybreaker]

Might be a good time to pull the ecu and check the board for carnage.

It's possible your old iac took out the drivers, or there's damage to the boards from acid that leaked from the caps.

We're starting to see the secondary failures from residual acid on boards that weren't cleaned/treated properly when they had the caps replaced years ago.

Post a picture if anything looks amiss, and one of the ecu guys can diagnose things further.

 

[vtecds1]

Are you running an aftermarket AFPR? Had similar problems because the diaphragm was shot.

 

[deez]

Give us a list of mods so we know what we are working with

 

[dmj]

Mods on this car Keydiver stage 3 chip 650 cc injectors , buschur/sx fpr, walbro 255 fuel pump.Hks 264 int/exhaust cams, evo 8 mas. Evo 3 exhaust manifold and turbo ported 2g o2 housing and CME 2 1/2 in exhaust. Boostx coil on plug setup. New oem Isc valve and o2 sensor and rebuilt alternator.When the idle drops I have noticed that the vacuum reading on the boost guage drops to almost 6- 8 in of vacuum .