So what does that mean?

I rebuilt the motor recently, with Atkins 3mm parts, silicone vacuum, HKS downpipe, PFC, and a few new parts. It started the first time, and needed no adjustments. It's run perfectly until a few weeks ago, when I took it down to work on the upholstery, pulling the stock radio/CD in the process.

I start it, accelerated warm-up is fine, but when at temperature, it pulses between 800-1400 rpm. I swapped the Idle Air Control Valve, same problem. I adjust the TPS (narrow=1, full=.44), through the PFC, but no change. Electrical loads and air conditioning appear to have no effect on the problem.

I unplugged the Idle Air Control Valve and the problem, along with the accelerated warm-up, disappears. It idles (without A/C) and runs as good as ever.

So where does one go now? What inputs contribute to the IAC actions?

Thanks for any help...

 

Usually the air adjustment screw at the base of the throttle body needs to be one half to one third of a turn out to fix this.

 

It's set 1/2 turn out, as per Chuck's recommendation.

It would seem that the problem should be directly related to inputs to the Idle Air Control Valve, as the problem disappears when it's not connected. I've seen people post saying "Disconnect the Idle Air Control Valve, and see what happens", but I haven't seen anyone recommend what to do next when it is the problem.

 

The ACV controls air flow from the air pump to the exhaust manifold and cat.
All of this works with the O2 sensor and O2 FB control. Changing air flow into the exhaust manifold affects what the O2 sensor reads (AFR) and affects idle.

Thus something is not adjusted corrrectly or not working corrrectly with the idle control systems.

 

Then would it make sense to disconnect the air pump, and see if it has an impact on the idle (good, bad, or indifferent)?

 

I went back to the beginning and disconnected the battery.

During the learning process, the PFC was fighting the pulsing and having some success, but it seemed to be most successful under the AC load. I raised the no-load idle to 900 and the idle smoothed-out. I lowered the idle to 800 and it's deceleration to 900 and still no pulsing.

Now the problem is, that's only masking the problem (probably better than running with the ISC disconnected), but the problem still needs to be addressed.

Does this help identify the real problem at all?

 

I gave you a better explanation on "The Other Site".

 

I believe he is talking about the idle speed control valve. Not the ACV.

To address the problem, it sounds like the ISC is hanging open when plugged in suggesting some type of electrical problem that opens the valve incorrectly. You may need to check the wiring. I am not going to pretend to be an electrical expert, but maybe someone else on here can tell you how to trouble shoot the problem.

 

On the other site I gave him exact info on all the systems/parts that affect idle, and he purchased my tuning notes which has more info.

Most engine using the ISC to control idle will die if you disconnect the ISC unless they were idling at very high revs.

 

Thanks all,

I've got some reading to do, but I'll probably be pulling the UIM when it's all said and done. The harness seemed pretty good when I put everything together, made an effort to re-wrap some of it, so I'm thinking it's probably not the problem (but I'll keep it in mind).