This is a bit long so I will try to make it as clear as possible.

I bought a 93 RX7 with a stroked 383 LT1. The engine would idle high and the car vibrated so much it was impossible to stay on the gas too long. After a year of messing with it, I found out the main bearings had gone or something so it was cheaper to get another engine. Since I already had a new T56, I decided to get another LT1. I got a good deal on a new fairly stock LT1. Along with that came a new optispark, new plugs, wires, alternator, injectors (fron the junkyard), throttle body and a re-tuned ECU with a fairly stock tune. The car still has a weird idle. I have to start it, it hangs around 2000 rpm and slowly (and I mean slowly) goes down to about 800. If I wait through this process and then drive the car, the idle is stable but on occasion will hang when coming to a stop (not often). If I start the car and get going, the idle will NEVER come down and will remain around 1600 rpm. When I get on it a bit hard, the CEL will come on during deceleration. If I stay below 4000 rpm, no CEL. When the CEL comes on, I can stop the car, turn it back on and it's gone. Of course, i ahve no tools to read the codes and would like to know what software you guys suggest I purchase. Problem 1.

A friend of mine let me use his ECU tuned for CAI, headers etc. A good match for my car. I plugged it in and the CEL came on. Not sure why. The car idled rock solid and the engine was WAY smoother until about 4000 rpm but there was a big torque and power loss. I was excited but after 1 day of driving, it seems the ECU learned to revert to a poor idle. In fact, the weather got cold and the car would completely bog down if you pushed the gas for about 1 minute, then all of a sudden, it would work right. Could it be a problem with the temperature sensor (the only thing I have not messed with since I bought this mess). I purchased a reman MAF and that unit will not work properly on either ECU's. Problem 2.

So this car has seen 2 engines, 3 ECU's, multiple used TPS, IAC, MAP, and a new MAF and still behaves the same. I was looking for someone in Denver to adjust the TPS, IAC and give it a proper dyno tune but there is NOONE here. My question is to make sure everything is set properly, what is the right order of things. Do I adjust the TPS voltage first, then the throttle blades? Do I check for specific voltages to minimize variable? A little troubleshooting guidance would be greatly appreciated. The car was completely re-wired using new wire and the best connectors I could get my hands on. Some new, some very close to new.

I appreciate everyone's help. I am also looking to prepare for modifications and want to get the engine to breath better up top. I am very disappointed that this thing falls on it's face at 4500 rpm. I currently have shorty headers with 1 high flow cat and a 3.5" cat back, along with a CAI and no accessories (except alternator). I have a fluiddamper balancer too. My car is right about 2700 lbs so needless to say I have plenty of torque. I just want this thing to keep pulling hard. I am split between doing heads, roller rockers and a cam or simply going with a supercharger. Advice appreciated.

Sigfrid

 

To tell you how to scan it, we have to know what year PCM you are using - OBD-I (93-95) or OBD-II (96/97).

As far as the throttle body, back down on the idle stop screw until you have the correct idle RPM (which will depend on the tune). Stock idle speed for an M6 is 800 RPM with the engine fully warmed up. When the engine is cold, the PCM elevates the idle speed. When the vehicle is moving, the PCM elevates the idle speed. Back the stop screw down slowly, until you get the correct idle (as read on a scanner - a "tach" isn't very reliable). With the correct idle speed, use the scanner to read the IAC counts. Should be in the range of 20-40 counts for a stock"ish" cam, maybe a bit higher for a more radical cam. After you get the idle and the IAC counts correct, check the TPS closed throttle voltage. Should be in the range of 0.20-0.90V. PCM doesn't care, as long as its in that range. There is no way to adjust it, unless you slot the screw holes in the sensor. Some people seem to feel a voltage of 0.50 or 0.67V is better, but there's really no basis for that.

 

Thanks for the feedback. I will follow this procedure next weekend and see how she runs. I have no clue what ECU I have since I have changed engines and ECU's a few times. Is there a way to tell on the ECU? Thanks again,

Sigfrid