rough idle. lurching. running warm
 

so my 94 z28 has had an issue for a while now that ive been slowly trying to repair. it has a rough idle and lurching while driving. it also seems to run a bit warm especially if i dont have the ac on. so far i have replaced the engine temp and gauge temp sending units, the egr valve. the thermostat.... it also has a cold air intake but im not sure that this started as a result of that or not. any input would be great as i am starting to beat my head on the wall... lol have a great day!

Re: rough idle. lurching. running warm
 

Scanned for codes? Are the fans coming on?

Re: rough idle. lurching. running warm
 

Re: rough idle. lurching. running warm
 

it also continues to the lurching when trying to maintain speed... i also replaced the throttle position sensor. forgot to mention that

Re: rough idle. lurching. running warm
 

also, lol, the egr valve was completely useless... so plugged with carbon the pin wouldnt even move. wich worries me too that there might be plugged lines somewhere else

Re: rough idle. lurching. running warm
 

Have you checked fuel pressure? Plugs? Wires? Coil? ICM?

Re: rough idle. lurching. running warm
 

no i havent.... only reason is that i know a tune up on this car is at minimum 800$. i dont have the equipment to do it all myself. i wish i did! do you think maybe its the omni spark? that was gna be my next guess but when yuou have all that ripped out isnt it just easier to do it all?

Re: rough idle. lurching. running warm
 

Do yourself a favor, and buy some tools. For the plugs, I am guessing you have a socket set. or know someone with a set. Wires don't take anything special either, other than taking the heat shields off(if they are still on there) Spend $30 on a cheap electric meter and do some testing(not just replacing parts because you think they are bad.) Autozone, last I knew, would loan you a fuel pump test kit(which includes a meter) There is a bunch of info on how to check all these parts with said equipment. If you get stumped ask for help here.

Make sure you are changing a bad part, before spending the money replacing something that is working.

Re: rough idle. lurching. running warm
 

The middle of the coolant temp gauge is 210-degF. It is normal for the engine to run at that temp, +/- 10degF. On an early production 1994 the first fan (driver side) turns on at 226-degF (or when the A/C is on) and the second fan comes on at 235-degF. The mark after the center mark on the gauge is 235-degF. On late production models, both fans turn on low speed at 226 and both fans go to high speed at 235. Look in the fuse/relay box under the hood. If there are two fan relays, it's early production. If there are three fan relays, it's late production.

http://shbox.com/1/fan_schematic_1995.jpg

The "lurching" description needs clarification. It sounds like you press the accel pedal, the engine hesitates/stumbles and does not fully respond, then after a bit suddenly starts to accelerate. Is that what you mean? Does the car have an automatic or manual transmission?

You have to scan for codes. It's makes a lot more sense, and is significantly cheaper than your current approach of playing "parts replacement roulette". There are codes that don't turn on the SES light. If you don't have access to a scanner, you can download FREE scanning software, called Scan9495, written by a member here specifically for the 1994/1995 LT1. You buy a cable, run a data log, and I can review it to see if there are any obvious problems. Checking the fuel pressure is always a good idea.

For starters:

- how old are the spark plugs and wires?

- how old are the O2 sensors?

- how many miles on the the engine?

- are there any performance modifications other than the cold air inlet?

- have you checked the rubber elbow between the MAF sensor and the throttle body for tears, or the bottom edge of the elbow not being fully on the throttle body?

There is no real "tune up" in the traditional sense. You need to systematically work through the diagnostics.

Re: rough idle. lurching. running warm
 

i do get all of that... but the sensors were cheap. and the egr was too ugly to clean. plug 6 is a bitch to get to... i think its six? im not going into this blindly, but i just dont have the funds to accomplish that right now or the down time on a vehicle.... but i understand what you are saying for sure. if i could. i would... just wondering if anyone had encountered such an issue and had found a good result. thanks!

Re: rough idle. lurching. running warm
 

wow ok cool! ill address..
-yes the accelaration is exactly how you say it is.
-the car has 108000 actual miles.
-aka i have no clue on the mileage of the o2 or plug wires. ide imagine theyre due to be replaced
- no mods other than cold air all stock
- the rubber elbow is new and secure between the maf and tb....
thank you!

Re: rough idle. lurching. running warm
 

I understand where you are coming from, and to answer your last question:" just wondering if anyone had encountered such an issue and had found a good result."

Yes, I have changed worn plugs, and my car ran better
Yes, i have changed burnt plug wires, and my car ran better
Yes, I have changed a bad optispark, and my car ran better
Yes, I have changed a bad fuel pump, and my car ran better.

The key to all the above statements, is the parts were bad, and were replaced with working parts.

I am trying to help you, not spend money on parts that are functioning. In order to do that you're going to have to do some troubleshooting.

Re: rough idle. lurching. running warm
 

Where are you from, maybe someone is local to you, and could help you with tools?

Re: rough idle. lurching. running warm
 

Did you replace the rubber intake elbow BEFORE or AFTER the lurching started? Air bypassing the MAF sensor due to the bottom of the intake elbow rolling under and not going fully over the throttle body can cause that problem.

Is the lurching only there when the engine is cold, only there when the engine is at full operating temperature, or all the time?

Scan 9495, being free, is cheaper than some of parts you've replaced, even when you throw in the cost of the cable.