Egr/rough idle
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Egr/rough idle
1989, auto trans, 49000 miles
I have had this car almost three years now and I still have not fixed my rough idle. It has a miss at idle, and at times I thought I had it fixed, but no luck. I have tested or replaced everything I can think of or read about. I have tuned it up several times and set all settings to factory. No vacuum leaks, burns no oil, no blown head gasket, and runs great above idle
I am now down to two possible things, I believe, but am still very open to suggestions
broken valve spring or leaky egr valve.
Ref the egr valve, I know it is normally closed at idle and gets no vacuum thru the electric selanoid at idle. I have checked this, and it appears to be working, how ever that does not mean the egr valve is not leaking when closed. The rough idle is sometimes better and sometimes worse. When it is worst the rpms fall in the 500 range. It idles much better when the idle rpms are in the 650 to 700. This is in park or drive. When I apply vacuum to the valve at idle, the idle gets worst at expected. I had this current egr valve replaced about 4000 miles ago when I had injectors replaced along with other things. Its been so long now I can not remember how good or bad it idled when I first got car. I have checked vacuum, and it is at about 17, except it has a very slight jump which seems to match up with the miss at idle. Like I said above, I have replaced everthing, sometime more then once, in the electrical side, wires, cap, rodar, coil, plugs, aic, cts, cleaned MAF, sea foamed thru intake, and added to gas and oil.
My question, it there a way to check for a leaky egr valve without removing engine parts. I would hate to go thru the process of removing parts, and replacing egr, and that not be the problem, not to mention I have never done it before.
I have had this car almost three years now and I still have not fixed my rough idle. It has a miss at idle, and at times I thought I had it fixed, but no luck. I have tested or replaced everything I can think of or read about. I have tuned it up several times and set all settings to factory. No vacuum leaks, burns no oil, no blown head gasket, and runs great above idle
I am now down to two possible things, I believe, but am still very open to suggestions
broken valve spring or leaky egr valve.
Ref the egr valve, I know it is normally closed at idle and gets no vacuum thru the electric selanoid at idle. I have checked this, and it appears to be working, how ever that does not mean the egr valve is not leaking when closed. The rough idle is sometimes better and sometimes worse. When it is worst the rpms fall in the 500 range. It idles much better when the idle rpms are in the 650 to 700. This is in park or drive. When I apply vacuum to the valve at idle, the idle gets worst at expected. I had this current egr valve replaced about 4000 miles ago when I had injectors replaced along with other things. Its been so long now I can not remember how good or bad it idled when I first got car. I have checked vacuum, and it is at about 17, except it has a very slight jump which seems to match up with the miss at idle. Like I said above, I have replaced everthing, sometime more then once, in the electrical side, wires, cap, rodar, coil, plugs, aic, cts, cleaned MAF, sea foamed thru intake, and added to gas and oil.
My question, it there a way to check for a leaky egr valve without removing engine parts. I would hate to go thru the process of removing parts, and replacing egr, and that not be the problem, not to mention I have never done it before.
Instructor
Joined: Jan 2015
Posts: 226
Likes: 22
From: Dade City Florida
Been chasing the same thing that just started on my 88. Just found this
Vett notes
C4 CORVETTE COMMON PROBLEMS:
This information was pulled from the internet and is just being passed on here to our C4 customers. We do not take any credit for this information.
Of all the C4 Corvettes that were manufactured in it's twelve year reign, the 1984 Corvette has been identifed as the Corvette most plagued with problems. As this was the first year for the C4, there were a lot of "unknowns" that were identified and corrected by the beginning of the 1985 Corvette's production. Still, the 1984 Corvette is one of the most available and most affordable Corvettes in the used sports car market today.
The following list of common issues is intended for individual reference only, and may not reflect the specific issues of every 1984 Corvette. This information comes from a variety of sources including the NHTSA Defects Reports pages. While the intent of this page is to identify the common issues pertaining to the 1984 Corvette (including the Collectors Edition and the Grandsport,) it is not an all-inclusive list and should be used for reference only.
MECHANICAL ISSUES
ENGINE (GENERAL)
When hot, the engine develops significant hesitation and a loss of power at high engine RPMs.
CROSSFIRE FUEL INJECTION
The CrossFire Fuel Injected V-8 Engine has a hesitation/rough idle during acceleration. This is a very common issue with crossfire motors. The stumbling is probably from a weak fuel pump, low fuel pressure, dirty fuel filter, a dirty fuel pump sock or all the above.
ROUGH OR ERRATIC IDLE
The erratic idle (both high and low) is more than likely caused by a vacuum leak. The main cause of this is that the top plate bolts become loose on the stock manifold and the throttle body shafts are worn out and leaking. The shafts go bad generally at around 50,000 miles and need to be bushed.
Another item that often causes rough or erratic idle is a bad coolant temperature sensor. It is the Coolant Temperature Sensor that screws into the front of the crossfire manifold and has a small plastic shield around it. Replace the sensor with the newer two pin weather pack type. Do not wrap the threads with Teflon tape iwhen installing the new sensor as the threads/sensor body provides a ground through the block.
A third, possible cause for rough or erratic idle is a bad oxygen sensor.
HEADLIGHT MOTORS
Headlight motors are unreliable and commonly break, failing to open/close the headlight. The headlights are operated by an electric motor and have a worm gear, which rides on a plastic gear to turn the headlights up when in use. General Motors used small plastic bushings inside the gears to act as a buffer for vibration and to smooth the operation of the lights. Replacement of these bushings will often improve the operability of the headlights and eliminate the headlight issue.
WIPER MOTOR
One common problem is the wipers on many of these cars are not properly adjusted to rest beneath the hood when turned off. When the wipers do not park correctly, they can scrape the black paint on the window trim, resulting in unsightly scratch marks on the trim and blemishing the aesthetic appeal of the vehicle.
TRANSMISSION
The 4+3 transmission is difficult to shift.
The transmission is known to leak at the seals.
Internal mechanical failure causes the transmission to tap when the vehicle is started in cold weather.
Automatic transmission known to bind and stick in reverse. It exhibits difficulty shifting between gears during extreme cold conditions - most especially from 1st to 2nd. Also known to have slippage between 2nd and 3rd gears. Other problem areas with the automatic transmission include difficulty shifting into reverse and the overdrive tends to to make clunking noise when engaged/disengaged.
REAR DIFFERENTIAL
Rear end of the car is noisy and is known to leak fluid.
FRONT SUSPENSION
Independent front suspension failure causes vehicle to have poor directional control and to wander when it goes over bumps in the road.
POWER STEERING/STEERING COLUMN/GEARBOX
Steering column failure results in poor directional control and wandering on smooth roads.
At times, steering seems to bind when steering wheel is being turned indicating/possibly causing severe damage to the gearbox.
Power steering reservoir cap leaks fluid throughout the engine compartment.
Rack and pinion steering locks up during cold starts or ambient temperatures. It has been reported that this particular rack and pinion failure is caused by defective neophene seals. As vehicle reaches operating temperature, the problem appears to correct itself.
EXHAUST SYSTEM
OEM Catalytic converters are known to fail, causing a "rotten egg" odor in the car.
BRAKES/BRAKING SYSTEM
Front brake mounting plates have been known to fracture, causing the caliper to rotate forward and jam against the dust shield. This, in turn, can cause significant brake failure resulting in other hazardous conditions including potential severe damage to the car as a whole.
EXTERIOR ISSUES
REMOVABLE ROOF
Removable roof top leaks around weatherstipping seal.
BODY PANELS
Fiberglass body is known to experience severe cracking resulting from stress on the body due to lack of structural braces.
INTERIOR ISSUES
THE DASHBOARD
The dashboard is known to short-circuit, resulting in intermittent operation of the dashboard. The result is a flashing dashboard - or - a dimly lit or a completely blacked out dashboard. The main reasons for this issue are: poor electrical grounds, corrosion on the terminals, or burnt out lightbulbs. To resolve this issue, one of three possible solutions exist. These are:
1.) One or, or as many as all four halogen 882 light bulbs may need to be replaced.
2.) Clean the 882 light bulb sockets.
3.) Check ground connections for dashboard to ensure proper grounding.
The additional power draw by the electric dashboard causes premature battery failure.
DOOR PANELS
Driver side door panels commonly crack on the inside as the direct result of poor holding design.
POWER WINDOWS
The power windows on most C4 Corvettes tend to operate excessively slow. After 1986, a replacement motor was introduced. However, there are now a number of after-market options available to replace the factory windows.
Misalignment of the window in its track causes scratching to occur on the glass surface of the window.
Passenger slide window is known to slide/fall down in its track at will.
POWER SEAT MOTORS
Power seat motors are known to fail, impairing the operator's ability to change the position of the seat.
REAR DEFOGGER
Rear defogger often fails to work.
OTHER ISSUES
A number of engine fires has been reported by 1984 Corvette owners. When conisdering purchasing a 1984 Chevy Corvette, identify if the engine has caused this type of fire.
Excessive squeaks and rattles throughout the car.
Seatbelt warning chimes often fail to operate.
Cruise control cable failure is known to cause engine runaway.
Vett notes
C4 CORVETTE COMMON PROBLEMS:
This information was pulled from the internet and is just being passed on here to our C4 customers. We do not take any credit for this information.
Of all the C4 Corvettes that were manufactured in it's twelve year reign, the 1984 Corvette has been identifed as the Corvette most plagued with problems. As this was the first year for the C4, there were a lot of "unknowns" that were identified and corrected by the beginning of the 1985 Corvette's production. Still, the 1984 Corvette is one of the most available and most affordable Corvettes in the used sports car market today.
The following list of common issues is intended for individual reference only, and may not reflect the specific issues of every 1984 Corvette. This information comes from a variety of sources including the NHTSA Defects Reports pages. While the intent of this page is to identify the common issues pertaining to the 1984 Corvette (including the Collectors Edition and the Grandsport,) it is not an all-inclusive list and should be used for reference only.
MECHANICAL ISSUES
ENGINE (GENERAL)
When hot, the engine develops significant hesitation and a loss of power at high engine RPMs.
CROSSFIRE FUEL INJECTION
The CrossFire Fuel Injected V-8 Engine has a hesitation/rough idle during acceleration. This is a very common issue with crossfire motors. The stumbling is probably from a weak fuel pump, low fuel pressure, dirty fuel filter, a dirty fuel pump sock or all the above.
ROUGH OR ERRATIC IDLE
The erratic idle (both high and low) is more than likely caused by a vacuum leak. The main cause of this is that the top plate bolts become loose on the stock manifold and the throttle body shafts are worn out and leaking. The shafts go bad generally at around 50,000 miles and need to be bushed.
Another item that often causes rough or erratic idle is a bad coolant temperature sensor. It is the Coolant Temperature Sensor that screws into the front of the crossfire manifold and has a small plastic shield around it. Replace the sensor with the newer two pin weather pack type. Do not wrap the threads with Teflon tape iwhen installing the new sensor as the threads/sensor body provides a ground through the block.
A third, possible cause for rough or erratic idle is a bad oxygen sensor.
HEADLIGHT MOTORS
Headlight motors are unreliable and commonly break, failing to open/close the headlight. The headlights are operated by an electric motor and have a worm gear, which rides on a plastic gear to turn the headlights up when in use. General Motors used small plastic bushings inside the gears to act as a buffer for vibration and to smooth the operation of the lights. Replacement of these bushings will often improve the operability of the headlights and eliminate the headlight issue.
WIPER MOTOR
One common problem is the wipers on many of these cars are not properly adjusted to rest beneath the hood when turned off. When the wipers do not park correctly, they can scrape the black paint on the window trim, resulting in unsightly scratch marks on the trim and blemishing the aesthetic appeal of the vehicle.
TRANSMISSION
The 4+3 transmission is difficult to shift.
The transmission is known to leak at the seals.
Internal mechanical failure causes the transmission to tap when the vehicle is started in cold weather.
Automatic transmission known to bind and stick in reverse. It exhibits difficulty shifting between gears during extreme cold conditions - most especially from 1st to 2nd. Also known to have slippage between 2nd and 3rd gears. Other problem areas with the automatic transmission include difficulty shifting into reverse and the overdrive tends to to make clunking noise when engaged/disengaged.
REAR DIFFERENTIAL
Rear end of the car is noisy and is known to leak fluid.
FRONT SUSPENSION
Independent front suspension failure causes vehicle to have poor directional control and to wander when it goes over bumps in the road.
POWER STEERING/STEERING COLUMN/GEARBOX
Steering column failure results in poor directional control and wandering on smooth roads.
At times, steering seems to bind when steering wheel is being turned indicating/possibly causing severe damage to the gearbox.
Power steering reservoir cap leaks fluid throughout the engine compartment.
Rack and pinion steering locks up during cold starts or ambient temperatures. It has been reported that this particular rack and pinion failure is caused by defective neophene seals. As vehicle reaches operating temperature, the problem appears to correct itself.
EXHAUST SYSTEM
OEM Catalytic converters are known to fail, causing a "rotten egg" odor in the car.
BRAKES/BRAKING SYSTEM
Front brake mounting plates have been known to fracture, causing the caliper to rotate forward and jam against the dust shield. This, in turn, can cause significant brake failure resulting in other hazardous conditions including potential severe damage to the car as a whole.
EXTERIOR ISSUES
REMOVABLE ROOF
Removable roof top leaks around weatherstipping seal.
BODY PANELS
Fiberglass body is known to experience severe cracking resulting from stress on the body due to lack of structural braces.
INTERIOR ISSUES
THE DASHBOARD
The dashboard is known to short-circuit, resulting in intermittent operation of the dashboard. The result is a flashing dashboard - or - a dimly lit or a completely blacked out dashboard. The main reasons for this issue are: poor electrical grounds, corrosion on the terminals, or burnt out lightbulbs. To resolve this issue, one of three possible solutions exist. These are:
1.) One or, or as many as all four halogen 882 light bulbs may need to be replaced.
2.) Clean the 882 light bulb sockets.
3.) Check ground connections for dashboard to ensure proper grounding.
The additional power draw by the electric dashboard causes premature battery failure.
DOOR PANELS
Driver side door panels commonly crack on the inside as the direct result of poor holding design.
POWER WINDOWS
The power windows on most C4 Corvettes tend to operate excessively slow. After 1986, a replacement motor was introduced. However, there are now a number of after-market options available to replace the factory windows.
Misalignment of the window in its track causes scratching to occur on the glass surface of the window.
Passenger slide window is known to slide/fall down in its track at will.
POWER SEAT MOTORS
Power seat motors are known to fail, impairing the operator's ability to change the position of the seat.
REAR DEFOGGER
Rear defogger often fails to work.
OTHER ISSUES
A number of engine fires has been reported by 1984 Corvette owners. When conisdering purchasing a 1984 Chevy Corvette, identify if the engine has caused this type of fire.
Excessive squeaks and rattles throughout the car.
Seatbelt warning chimes often fail to operate.
Cruise control cable failure is known to cause engine runaway.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
On my 86' it took me a few years to sort out the idle as well. One of the big items was actually the Harmonic balancer. The rubber ring had started to slip and this moved the timing mark. When I would set the timing to 10 degrees it was actually at 14. Replacing the balancer fixed this.
I also did a smoke check on the intake to find a vacuum leak.
There were numerous sensor replacements as well, and I set the base idle.
All of these together got the idle to where it is pretty good, and I have not bothered chasing it further.
I also did a smoke check on the intake to find a vacuum leak.
There were numerous sensor replacements as well, and I set the base idle.
All of these together got the idle to where it is pretty good, and I have not bothered chasing it further.
