92 LT1 Rough Idle (Consistent)

[bucket]

On my 93 after I throughly cleaned the egr and was satisfied it was not malfunctioning I then ran the diagnostics from the fsm I have for the egr vacuum solenoid and found it to be bad. New part installed and the car ran much different because the vacuum was allowed to make the egr function correctly. And while I have mentioned vacuum check all the hoses and connectors for cracks or leaks with the mileage and age of the car it is possible you simply have a vacuum problem. I picked up about 3 feet of different size vacuum hose and then jumped around the vacuum hoses on the car one at a time until I found the ones that were leaking The first time I jumped the throttle after that I thought I had added 100 HP to the car.

..

nice car

 

[93Rubie]

***Update***
The car was hard to start this morning, this afternoon was worse. The car took .75 seconds this morning whereas this afternoon was like 1.0 second. [I am counting this like 1-mis-sis-sip-pi]

Not to belittle your situation, but that doesn't sound like a hard start to me. Maybe for a modern Fuel Injected car, that we are SO used to starting right away, all the time, running perfect, etc...we forget about actual hard starts with oh say a carbonated car from years gone by. I can hear my uncle trying to start his chevelle sometimes, he cranks on that thing for minutes, until it starts. (Not continuously, starters dont like that.) That car is SO cold blooded its not funny.

 

[KANE]

***Update***
The car was hard to start this morning, this afternoon was worse. The car took .75 seconds this morning whereas this afternoon was like 1.0 second. [I am counting this like 1-mis-sis-sip-pi]

Not to belittle your situation, but that doesn't sound like a hard start to me. Maybe for a modern Fuel Injected car, that we are SO used to starting right away, all the time, running perfect, etc...we forget about actual hard starts with oh say a carbonated car from years gone by. I can hear my uncle trying to start his chevelle sometimes, he cranks on that thing for minutes, until it starts. (Not continuously, starters dont like that.) That car is SO cold blooded its not funny.

Great point!

My Trans Am's LT1 fires right up when it is warm. However, if it has been a few hours- it does take a second to crank.

Remember- the computer calibrates the fuel curve in part based upon the temperature of the engine. Colder engines get more fuel when starting & a warm engine starts quicker.

I guess the question is whether or not that rough idle is present when it is warm and continuously running. Is that the case?

 

[John Robinson]

What Schrade Said

This is my version of the highly technical cleaning procedure for the EGR

When you had the egr off did you test the pintle for leakage? The test is easy just put some fluid into the top of the pintle chamber and it should not leak through if the pintle is sealing correctly. It the fluid does leak through then you have to clean the pintle sealing surface. The best way I have found to do that is to get some Easy Off oven cleaner and spray it all around the pintle and be sure to push the pintle down so the cleaner gets onto the sealing surface of the pintle. Let it sit for 20 to 30 minutes and continue to put cleaner on it to keep it wet. Now take and wash the oven cleaner off with warm water (this is best done when the wife is not home to see the mess before you clean it up)and retest the pintle for leakage. If no leakage then you are good to go back on but if it leaks repeat the cleaning and if you can get some old dentist tools so you can scrape the pintle base. You can push the pintle down and us a pencil or bolt to hold it open by putting it through the bottom of the egr to hold the diaphram open.

 

[92BlackVette]

This is my version of the highly technical cleaning procedure for the EGR

When you had the egr off did you test the pintle for leakage? The test is easy just put some fluid into the top of the pintle chamber and it should not leak through if the pintle is sealing correctly. It the fluid does leak through then you have to clean the pintle sealing surface. The best way I have found to do that is to get some Easy Off oven cleaner and spray it all around the pintle and be sure to push the pintle down so the cleaner gets onto the sealing surface of the pintle. Let it sit for 20 to 30 minutes and continue to put cleaner on it to keep it wet. Now take and wash the oven cleaner off with warm water (this is best done when the wife is not home to see the mess before you clean it up)and retest the pintle for leakage. If no leakage then you are good to go back on but if it leaks repeat the cleaning and if you can get some old dentist tools so you can scrape the pintle base. You can push the pintle down and us a pencil or bolt to hold it open by putting it through the bottom of the egr to hold the diaphram open.

I am going to vacuum test every line possible and then clean the EGR valve like you said.

 

[Schrade]

I don't think you have vac leakage; EVERY internal combustion engine will lope idle with a vacuum leak. 30 year old lawnmower (which my new neighbor has (with leak), or a NEW car on the lot 0 miles.

Once you put OEM chip back in, all baseline parameters will have to get back near OEM spec. One of them you can do by unplugging the TPS with the battery connected, and the ignition ON (motor off of course). If it's the same with other sensors, I'm not knowing.

And with a problem, some parameters will not go to spec, but they'll show on a scan, and then the problem will stick out like a sore thumb uh huh...

 

[John Robinson]

I don't think you have vac leakage; EVERY internal combustion engine will lope idle with a vacuum leak. 30 year old lawnmower (which my new neighbor has (with leak), or a NEW car on the lot 0 miles.

Once you put OEM chip back in, all baseline parameters will have to get back near OEM spec. One of them you can do by unplugging the TPS with the battery connected, and the ignition ON (motor off of course). If it's the same with other sensors, I'm not knowing.

And with a problem, some parameters will not go to spec, but they'll show on a scan, and then the problem will stick out like a sore thumb uh huh...

I would basically agree with you except in my experience The malfunction of the vacuum switch for the egr was causing it to not operate properly and therefore it was causing the egr to be open at idle when it was supposed to be closed. As for checking the other vacuum points and hoses again the connector on the vacuum valve under the fuel rail cover on the passenger side of the engine had the connector cracked from heat and age and when I replaced it not only did the cruise work better and the heater controls but the engine. I guess in my case what I did was to look at those parts as consummables and replaced them because it was the cheapest thing I could do. When your as cheap as I am you do everything you can think of to eliminate buying those mortgage breaking parts. And since I am retired it keeps me out of the house during the soaps on TV

 

[92BlackVette]

I happen to have a vacuum pump, vacuum gauge, FSM, and 30 minutes of extra time when I get out of work today (who works on Saturdays!), so I will entertain 6E3-C7-5 in the Driveability and Emissions in the 92 FSM. I will provide the forum with Hg Vacuum numbers.

Part of the test indicates that I need to: "ground diagnostic 'test' terminal". I assume this means I need to hook up my Actron code scanner.

*****

I know the EGR system gets its numbers from the CTS, IAT, TPS, and MAP. Could I trouble you for the definitions of the TPS, and CTS please.

 

[John Robinson]

Tps

TPS is the Throttle Position Sensor.

Hope this sheds some light on the tps for you

​

Throttle Position Sensor (TPS)
Copied from 1993 Service Manual​

The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts
from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.

I used a couple of straight pins through the wires to hook the meter on

​

The CTS per my FSM says it is the Closed Throttle Sensor and is part of the KS (Knock Sensor) circuit.

 

[KANE]

CTS= Coolant Temperature Sensor

This is somewhat oversimplification, but the main points are valid....

This sensor is used to determine the temperature of the engine by way of its coolant. The ECM uses this data- along with other pieces of data- to set fuel needs, spark advance, etc. It also uses the CTS info in part to move the car into open or closed loop as needed.

 

[92BlackVette]

I am still working on it, but I vacuum leaks for sure.

 

[Steve40th]

Two things, I am not reading the whole post, just the first part. Your injectors OHMS are way high. They shouldnt be more than 16 ohms for a 92 LT1.
And replace or ohm check your IAC as it will cause a crappy idle yet you will get no codes from ECM, and a datalogger will only show you what the ecm is telling the IAC to do.
http://www.youtube.com/watch?v=_g8PdrT0MCU&feature=player_embedded#
http://www.youtube.com/watch?v=FEFLtw3T_j0
Disconnect your harness at each injector and clean with sensor cleaner and put some dielectric grease in there.

 

[Schrade]

I happen to have a vacuum pump, vacuum gauge, FSM, and 30 minutes of extra time when I get out of work today (who works on Saturdays!), so I will entertain 6E3-C7-5 in the Driveability and Emissions in the 92 FSM. I will provide the forum with Hg Vacuum numbers.

Part of the test indicates that I need to: "ground diagnostic 'test' terminal". I assume this means I need to hook up my Actron code scanner.

*****

I know the EGR system gets its numbers from the CTS, IAT, TPS, and MAP. Could I trouble you for the definitions of the TPS, and CTS please.

Yup - either the Actron, or the super high tech version:

placed strategically right here (ALDL interface):

 

[92BlackVette]

Th EGR Solenoid was shot, when energized the vacuum would quickly bleed out before it could pass through the device (internal leak). For example: with a gauge on one end and a vacuum pump on the other; [OEM solenoid] when pumped to 10 Hg of vaccum it would hold, not energized, and when energized it would bleed before the vacuum gauge could register a vacuum. I bought a new one (solenoid) and it turns out it would hold a 10 Hg vacuum when energized, and read as such on the vacuum gauge on the other end. I fixed numberous vacuum lines as well, so they are all confirmed good at this time. Checked both left and right banks.

I have tested the EGR valve, cleaned also.

That is probably part of my 152,000 mile problems, but I am not done testing.

Back to the fuel injectors: I have a Mickey Mouse tester and it only allows for the following ohm settings: 1K, x100, x10. The readings I posted are at the x10 setting so maybe I need to invest in a better reader?!?!?

 

[92BlackVette]

otflThanks for everyones help

I think we nailed it with the EGR Vacuum Solenoid!

It has been running excellent for 2 days so far.