my z28 is idling rough at low rpms and gets better at higher rpms. it also backfires when taking off. i have replaced the plugs and the egr sensor, but didn't help the problem.

 

Disconnect an O2 and see how it runs after it gets up to operating temp. If it runs better, you have a closed loop problem.

 

I know it sounds laughable, but check the plug wires, I had a very similar problem with my formula recently. Especially check them @ the opti, my plug wires were on, but not on and connected good enough, when u put the wires on did u use dielectric grease? When I lived in montana we never used the stuff, dry mountain air, moved to se texas and down here plug wires rust, coil tips rust without it. High humidity I guess. Ur car is a year that u can retrieve any codes by enabling the self diagnostic mode, so if u don't have a scanner or a reader if it puts out an ses u have a way of getting it @ least, wish my 94 could do that, the jumper trick doesn't work for 94's. Also u might check the injectors, the fuel filter been changed recently? Vacuum leaks. It could be a ton of stuff, check the coil, easiest way is have it tested, or slap a new one on, if it still runs the same, return the coil. Not the way I do it but u gotta do what works right? Also the egr, u said u replaced the sensor? Do u mean the valve, or the solenoid? Check and make sure u connected the vacuum lines, and did so correctly, look for cracks or vac lines not well connected, the little black line sometimes isn't in the black elbows far enough. Thatll get u started @ least

 

Seeing as how the OP has a '95, he can't jump the pins on the diagnostic port.

 

I never said that he could, I said only that I couldn't, go to shoebox's website, it'll tell u how to put a 95 into self diagnostic mode, but thanx for tryn to set that straight, a 95 has the 1.5 or obd2 connector with obd 1, the 94 while still a 12 pin and obd 1 is not able to be jumped using pins 5&6, all that happens is ur fans come on, which can be handy between rounds @ the track.

 

I think you are mistaken about putting the car in self diagnostic mode to get the engine codes. If that were possible, then anyone who's been around this board very long would know that trick, and also know the 95 is OBDI with an OBDII connector. Are you sure you didn't see how to put the 96 and 97 into diagnostic mode for the Body Control Module?

 

That's what I said just in reverse on the obd1. With an obd2 connection as far as the diagnostic I wll check u may b right

 

Yep your right, however I did find a way for a person with a 95 and the obd 1.5 setup or as I said before the obd2 connector, and obd 1 in the car, to hook it up to an obd1 12 pin scanner and get the codes for the ses. Let me know if u r interested, and I apologize, because it didn't really apply to my car I didn't pay attention to the details, it is the bcm not the pcm codes u can get a 95, or 96, see I'm doing it again, to display. My error.

 

Most everyone here knows how to hook up a 12-pin OBD-I scanner to a 95's 16-pin connector - Shoebox showed us about 10 years ago:

http://shbox.com/1/xraycable.jpg

The 95 does not use OBD-1.5. Only the Corvette LT1 used that system, with the single after-cat O2 sensor. There is virtually no difference between the 94 and 95 F-Body PCM's..... they are both OBD-I. The 95 just has the oddball 16-pin connector.

And you can not read the BCM on a 95 in any way. The 95 does not have a BCM. The BCM was only added in 96.

 

The way I was told is that 1.5 was as u said an obd 1 car with an obd2 connector, a chevy mechanic said that was what they called it, I don't know if he was misinformed, and for the bcm, didn't I correct that? And I was referring to anybody that didn't know about using an obd1 scanner on a 95. Sorry if it seems otherwise, but I'm aware that the moderators, and most of the people that have been on here for a while know what they're doing on these cars. I apologize for the misinformation once again regarding the bcm code retrieval on a 96, and for not having paid more attention to it.

 

But since we're on the subject, what are the differences in obd1 and 1.5 for the vette? The addition of more sensors9 the pcm receiving moe data as per the monitoring of the car? I would like to know, if I'm wrong I may as well learn from the mistake.

 

Corvette OBD-1.5:
-third "after-cat" O2 sensor
-TPS interfaces directly with EBTCM
-secondary AIR pump circuitry revised to allow PCM to detect missing pimp
-capable of 86 to 131 3-digit diagnostic codes
-16-pin, with pin 2 for J1850 bus

It actually was a partial upgrade to OBD-II standards. The F-Body stayed at the OBD-I level through the entire 95 model year.

The best reference for comparative purposes is the Charles Probst book "Corvette Fuel Injection & Electronic Engine Management". It actually is endorsed by GM, and given a GM part # (12497977). Unfortunately, there are a couple of major defects... like switching the descriptions of "BLM" and "INT" on page 34.