I will try to make this short and to the point. I have a 91z28 with 350tpi. i just put a new 350 in it and used all old parts. i put all new sensors in. mods are in signiture. Here is the problem. I am always smelling fuel vapors but there is no leaks at all. the engine lopes at idle and stays at 1500 PRMs all the time. I just installed a air fuel ratio gauge and it goes all over the place. it only reads right for about 3 minutes in the morning.then it goes into the low red and then yellow. as the engine lopes the gauge lopes as well. when the rpms go up the gauges reads in the yellow and reads red when engine lope goes down. the engine doesnt lope all the time though. just when it wants. fuel pressure is set 43psi at idle with vaccumm connected. fuel pressure gauge reads fine and is not effected by engine loping. What should I be looking for to track this problem down last resort is a shop

PS another problem: the car is hard to get started sometimes. it will fire up and run like its on 3 cylinders for a second until I rev it a little then it is normal. this only does this 6 out 10 times. when it does this though the smell of fuel vapors is really strong. I did put in a Holley fuel pump when engine was changed last year. I am running LT1 injectors and LT1 cam if it matters and there is no smog equipment at all.

PS engine backfires when its cold when I decelerate in gear. its do this when engine is up to temp

 

The fuel pressure may be a bit high with LT1 injectors.

As for the "lope" it certainly shouldn't be from the mild stock cam. You could perform a power balance test to possibly see if any of the used injectors are not flowing or spraying correctly.

If you are certain the ignition system is functioning and you have good compression on all holes, you need to perform a power balance test to locate the offending cylinder(s). I had a similar problem with my TPI and the test isolated the dead holes.

To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.

Compare the RPM drop at each cylinder. Don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate or if it has a poor spray pattern.

NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.

This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank and a "professional" cleaning at the dealer with the fuel rail system, all with no improvement.

As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.

 

Sounds like leaking injectors to me.

They would give a rich idle (which a cold eng would like for a short period).
They would flood the intake with fuel a few mins after shutdown.
Fuel would evaporate after a few hrs.

 

or a huge vacuum leak. it would cause air/fuel to jump around like crazy, and would make a super-mild near stock cam lope like a pro-stocker. Check EVERYWHERE for vacuum leaks!

 

thanks for the tips. Vader, I will try the power balence check you are talking about. I am going to check timing, reajust the IAC and TPS befor doing this though. I am going to pull the plugs to. I just wish my car would idle at a normal RPM. it makes it almost impossible to find other problems.