Thank that you in advance for any advice that may be given. I have a 1991/740 Regina. Several months ago it started taking 2 or 3 attempts to get her started when she had been parked over night and began idling ruff. I repalced the dist. cap, rotor, knock sensor, O2 sensor, and removed and cleaned the throttle body. I had gotten codes for knock and O2 sensors. Now she idles at about 500 rpms in drive and when I accelerate all is fine till 1800 -2000 rpms when she hesitates, almost no power. If I get over 2000 rpms she takes off like a rocket. Runs fine if I can keep her from going under 2000 rpms when she shifts. I have also checked timing, with a light, and appears fine. Plugs and wires do not have 6000 miles on them. I at this point am not sure which way to go on this. Again any help would be appreciated.

 

If there's no codes. Your going to have to analyze every sensor and system while it's acting up. Look for threads on the same symtop which will give you direction on which systems to start checking. If it's happening all the time you going to have an easy time figuring this out.

 

Thank you guest01. I will continue to do more research. I just checked codes again and got a 2-3-3....missing IAC signal. Removed cleaned and tested (applied power from battery) the IAC and it seems to be working properly. Will have to find where to check signal to and from IAC motor. I also removed vac. hose to the front of FPR and it started idling about 2 or 3 hundred rpms higher putting it in the range it has been for the last 22 years I have drriven her. I will have to learn to be much more proficient with a volt meter it sounds.

 

Can't say that I'm familiar with that code. Most of time good idea to track down the problem of the code first with driveability concerns.

On a MAP system vacuum leaks raise the idle. Normal. FPR not bad.

PS: voltmeters work and have there place. But real diag is done with at least a graphing meter or scope.

 

the IAC, one pin of the connector is wired to switched power (12V when car is on), and the other side is intermittently grounded by the ECU to modulate the idle, so if you look at this side with a meter, you'll see an AC signal, if your meter has a "Duty Cycle %" mode, this would go up and down as its modulating the idle speed. once the throttle is off the idle switch, then the IAC isn't used at all, so its a good thing to test the idle switch with an ohm-meter to verify its closing at idle, and opening as the throttle comes off idle.

 

yeah, that signal is not AC volts.

 

right, its a square wave with a duty cycle. the 'open collector' output of the ECU needs to be connected to a 'pull-up' (like the ICS itself) before you'll see anything but noise on it.

its a fairly low frequency signal, a few pulses/second or something.