Nagging Fuel Mixture Issues

[Enigma_Owl]

I have a '71 3.5 Coupe that has two (possibly related) engine management problems. When I first got the car nearly 2 years ago, I did notice that on cold start it would go straight to an idle at about 800 rpm (no high 'warm-up' idle with gradual reduction to normal idle). It continues to do this now, with the car sometimes having a rough start and stall.

The second problem developed about 6 months ago with the car riding rough below 2,000 rpm after warm-up; making the car really sluggish from a standing start and even stalling while stopped in gear if the coolant temperature is above 180. I was sure that it was either a ECU or sensor problem, but neither of these things have proven to be the culprit.

In this time I have had:
-Map Sensor replaced (with a new air filter, plug cleaning, and idle and injection adjustments)
-Distributor Rotor replaced
-Aux. Air Regultor replaced
-Temperature Sensor
-New injectors
-ECU and 2 relays replaced (below the computer, with a second idle adjustment)

Now the two problems persist, but are manageable. My mechanic says that I have no vacuum leaks and my wiring harness looks fine, but he's at a loss as to what could still be the problem.

HELP!!
-Sean

[Tom Hanson]

Check the air sensor on the air filter and the water sensor that looks just like it. Also check the manifold pressure sensor, the throttle switch, and the cold start sensor. So many components that can go bad on this system.

[ja17]

Hello Sean,
Don't forget the basics before going to the expensive parts. The car must be in good tune, timing plugs etc. Always make sure that the fuel delivery system is in good shape. The fuel filter should be clear. One good place to start is a fuel pressure check on the running engiine. The sysem must have the correct fuel pressure and supply to function correctly. As far as the cold start missing look at the thread on the "trigger points".
Check the ignition timing and the warm-up unit on the intake which controls cold idle air.

joe Alexander
Blacklick, Ohio

[Enigma_Owl]

Hi Tom and Jack,
Well, I just got the car back from a different mechanic (who consulted with the first mechanic and Peter Krausert; thanks for the tip Tom :D ). It appears that I did have a vacuum issue (only about 8psi when it should be between 17-22psi); which was throughing everything out of whack. A couple of my valve seals were also too tight. Still, the main culprit seemed to be a fouled throttle assembly that needed a thorough cleaning. Once that was done, the vacuum came up to 13psi and was responsive to the computer adjustments. I also had a breakerless ignition system installed while he was at it.

The vacuum still isn't where it should be (my mechanic is worried that I have the start of a rings problem), but the car is now performing BEAUTIFULLY! Thank you both for your tips!