I have a 91 stock 305TPI motor (VIN F-7730 ecm)the only changes to the engine have been a high volume oil pump, a set of Sanderson headers, a heated o2 sensor and the cylinder heads have been rebuilt. The engine does have all the emmision devices bypassed i.e. egr, air dirvert etc. The ecm does not contain any trouble codes but I did note that the fuel pump voltage seemed a little high at 14.2 volts.

The problem is when I start the car it will idle briefly than the idle drops and the engine begins to surge. If the idle drops enoughy the engine will stall. If I hit the accelarator the engine springs to life and will try and idle again but the problem reoccurs.

I have checked the fuel pressure, fuel pressure at idle is around 38lbs. With the engine off it is about 42lbs.

I have measured and adjusted the new TPS switch and I have measure the IAC motor to ensure it is in specs. I tested each injector to verify resistance all injectors are 15.9-16.2. I have replaced the MAP sensor as well.

I removed all the spark plugs and regapped all the plugs, I did find one cylinder that the plug was black and wet. I assumed I had a bad injector, so replaced all my injectors with bosch III but the problem is still there.

I can't get the vehicle to idle long enough to adjust the valves, timing, etc.

This engine is in a custom car I have been building for many years and this is my first attempt at a fuel injected engine, any assistance is greatly appreciated.
I apologize for any grammar errors as i am typing this from the garage.

Thanks
msaby@fast.net

 

sounds to me like you could have a vacume leak. check to ensure all the hoses are connected correctly and there are no cracks holes or cuts.

 

Okay I removed and plugged all non essential vacuum lines, I still have the same problem. I disconnected the alt because i read a post indicating voltage may play a part with inconsistance idle.

When I unplug the timing connector the engine will idle, it still surges but it does keep running. The engine is still running rich though.

While the engine continued to run I sprayed a little carb clear around each injector, all the manifold gaskets, the vacuum lines and the idle did not change.

I checked the cap and rotor, the ignition module was replaced already.

Any assistance is greatly appreciated
Mike

 

did you do any prom changes? since you said no egr..and changed injectors..were they the same size injector...

 

Exactly. What size Bosch injectors did you install? If larger then 19# then the idle is to rich and loading up. You will need a new tune.

If 19 pounders, have you done the IAC adjustment? There is a thread here on Third Gen on how to do it.

 

No prom changes, I have a egr bypass inserted into the connector to disable it, The injectors were replaced with the bosch III and they were the 19lb injectors same as oem.

I did check the IAC by removing it and then measuring the length to ensure it was within spec and then I reinstalled it.

 

how many miles on the car? I would adjust the IAC..then if still persist I would start looking at the fuel pump...I had one do that..and the fuel pump isolator was replaced with the wrong kind of hose,and the gas was swelling up the hose so it wasnt getting enough fuel..

 

I did already adjust the iac motor and i replace the fuel pump twice. I haven't even driven the car yet. The motor had low miles but was freshened up before it was installed.

 

if you can unhook the timing connector, I would say test your pickup coil in your distributor...

 

I agree check under the distributer cap also look at the pole piece see if any are broken. They rust pretty bad around here in the northwest at least. Also check your CRK fuse if you have a bad cold start will blow a fuse and will cause the same problem as a vaccum leak. Better to just block the cold start.
http://www.rockauto.com/catalog/raframecatalog.php
http://www.rockauto.com/catalog/raframecatalog.php

 

Problem solved, When i removed the distributor to reprime the engine I must have re installed the distributor a tooth off and the ecm was trying to compensate for my stupidty. I reset base timing and the engine idle is perfect. I did however develop a code 54. I have to do a search on the forum for that one.

Thanks for all of your help

Mike