Idle/response problems

[Cudabob]

When I first start the car up(1988 coupe)the idle is good and the throttle response is good.....then after a short time the idle drops and the throttle response is crappy.Any idea what the problem is?

 

[Hib Halverson]

When I first start the car up(1988 coupe)the idle is good and the throttle response is good.....then after a short time the idle drops and the throttle response is crappy.Any idea what the problem is?

With that limited description of symptoms, it's difficult to offer any useful information.

It could be a fuel system problem. It could be a vacuum leak. Could be ignition.

Is the check engine light on?

Do you have a Factory Service Manual?

 

[Cudabob]

With that limited description of symptoms, it's difficult to offer any useful information.

It could be a fuel system problem. It could be a vacuum leak. Could be ignition.

Is the check engine light on?

Do you have a Factory Service Manual?

I have checked out the fuel system with a guage and all is good.I checked all vacume lines when the code 32 came up and repaired a line then the 32 went away.The car has a fresh cap/rotor/module.I am wondering that maybe the car is messing up when it goes to open loop?In this mode the O2 sensor helps control fuel?Is it a possability that the o2 is gone?Right now there is no codes.Does the car need to be driven to activate the speed sensor to learn idle?

 

[boomdriver]

YES...
when stone cold it waits to read temps and other sensor input. On my 87, at 148 degrees it cycles into its normal run mode in open loop. Below that it will idle as low as 450 rpm but its rough. Like clockwork it will up-idle to 650 to 700 at 148 degrees, everytime. However, if I set the idle TOO low, it may stall and die if just sitting there idling, BUT if I drive it at any temp, that sets the idle and I can then sit at a stop-lite while in gear (auto) without a problem. There are certain functions in the ECM that have to see several seconds of movement over 30mph to set a base to operate from. If I remember correctly the IAC is part of this and it has to run these cycles everytime the battery is disconnected or ECM power is interrupted.

Your o2 sensor could be old and dirty sending poor signals. It has as much to do with fuel as anything else. Some hardcore tuners use a little electronic gadget to manipulate the o2 signals to get extra performance.A "race" setting for a bit more fuel and a "normal" setting for higher MPG and better economy. So it does matter lots to fuel control. The IAC could be (likely) dirty and not performing well. To clean an IAC valve/motor is more hassle than to replace one for around $25. To replace an o2 sensor is a little more money, but it will probably help.
You installed a new ignition module? Delco?
Some after market ign modules are generic and not "vette only" delco. I had used a parts store module in the past that created all kinds of symptoms, missing, hesitation, idling issues. I replaced with a new Delco unit and all the problems went away. Same goes for wires.

 

[Cudabob]

YES...
when stone cold it waits to read temps and other sensor input. On my 87, at 148 degrees it cycles into its normal run mode in open loop. Below that it will idle as low as 450 rpm but its rough. Like clockwork it will up-idle to 650 to 700 at 148 degrees, everytime. However, if I set the idle TOO low, it may stall and die if just sitting there idling, BUT if I drive it at any temp, that sets the idle and I can then sit at a stop-lite while in gear (auto) without a problem. There are certain functions in the ECM that have to see several seconds of movement over 30mph to set a base to operate from. If I remember correctly the IAC is part of this and it has to run these cycles everytime the battery is disconnected or ECM power is interrupted.

Your o2 sensor could be old and dirty sending poor signals. It has as much to do with fuel as anything else. Some hardcore tuners use a little electronic gadget to manipulate the o2 signals to get extra performance.A "race" setting for a bit more fuel and a "normal" setting for higher MPG and better economy. So it does matter lots to fuel control. The IAC could be (likely) dirty and not performing well. To clean an IAC valve/motor is more hassle than to replace one for around $25. To replace an o2 sensor is a little more money, but it will probably help.
You installed a new ignition module? Delco?
Some after market ign modules are generic and not "vette only" delco. I had used a parts store module in the past that created all kinds of symptoms, missing, hesitation, idling issues. I replaced with a new Delco unit and all the problems went away. Same goes for wires.

Well I changed the o2 sensor,cleaned the ground straps and re-installed,the module is a delco unit(new).I have it hooked up to a computer and I am getting a code 32 and the INT and BLM numbers are higher than normal(sensing a lean condition).I have checked all the vacume lines...........any ideas?

 

[boomdriver]

Code 32 is EGR in my book...That could be as simple as a dirty plug on the EGR solenoid, but more likely, it may indicate the EGR valve is stuck and adding exhaust gases or not, possibly creating a "lean" condition that the scan is seeing.

If you can get the EGR vac line to the valve itself, do a vac test first to see if it even operates. A skilled tech can use a mirror to see if the valve is actually moving when vacuum is applied.
These EGR passages get extremely crudy and almost closed with thick carbon build-up. Often cleaned with a bristle brush type drill attachment. Carb & choke cleaner finishes the cleaning. If the valve is functional, the valves plunger can be cleaned as well. My rule of thumb is replace if it has to be pulled unless something is unreasonably expensive, then attempt repair. An EGR valve is not very costly but it is a little bit of a hassle to get at. I even relocated my EGR solenoid to a valve cover where both the electrical plug and vac lines were now accessable.. I have had a failed EGR in the past but I do not recall what the code was.

 

[LLC5]

Well I changed the o2 sensor,cleaned the ground straps and re-installed,the module is a delco unit(new).I have it hooked up to a computer and I am getting a code 32 and the INT and BLM numbers are higher than normal(sensing a lean condition).I have checked all the vacume lines...........any ideas?

Just to be clear, open loop is when the O2 sensor has no control on EFI, closed loop is when it does. I would go after your EGR code and make sure it is fixed properly first as the EGR system is not supposed to be activated until the engine is warm and that appears to be when you are experiencing your problem.

 

[gmjunkie]

Just to be clear, open loop is when the O2 sensor has no control on EFI, closed loop is when it does. I would go after your EGR code and make sure it is fixed properly first as the EGR system is not supposed to be activated until the engine is warm and that appears to be when you are experiencing your problem.

 

[Cudabob]

I did a vacume pump test on the egr valve and it doesn't hold any vacume so I guess I have found the problem.I ordered a new egr valve and the upper intake gasket set,is there anything else I should replace under the intake plenm?

 

[boomdriver]

I would replace any vac lines under there, make sure the electrical is wrapped and in place, clean the EGR solenoid connection and thats about it. A little house keeping while you have the plenum off.

One trick that I learned over the years with the runner to plenum gaskets (and throttle body) is to wipe a small amount of 'never-seize' on both sides. Wipe away any excess. This will prevent the gasket from glueing itself to the metal and eliminates the need to scrape it off next time.
Glad you found the/a problem. Hope thats all it is.

*** NOTE ****
One of the EGR mounting bolts will require an offset wrench of some sort. I forget exactly what works. I remember the standard box end would not fit over it, and a socket won't fit under the EGR diaphram. One of the 2 bolts was awkward to remove. You may want to do a visual inspection of the EGR tube while the plenum is off and see if that needs to be replaced while you have good access. If the insulation wrap is still good,its probably ok. That tube will eventually rot thru and make embarrassing noises from your engine bay besides blowing hot exhaust gasses onto various things...OBSERVE how it is mounted on BOTH ends before messing with the tube...Some models had a crimped on end that is impossible to replace. The upgraded EGR tube had a bolted flange type end on the top and bottom. If you have one that has the crimped on clamp, let a shop deal with it when the time comes! PITA. You can get the crimp on clamp, just not the tool to crimp it. :~)

 

[Hib Halverson]

Some early C4 EGR systems have a temperature swtich which, if it fails, will cause a DTC32.

Sadly, finding replacement EGR temp switches is extremely difficult.

 

[aklim]

Have you thought of getting a block off plate and a chip that is set not to show the Code 32?

 

[Cudabob]

Have you thought of getting a block off plate and a chip that is set not to show the Code 32?

I have to pass emmisions here so I will replace the egr,IAT switch and hopefully that will fix it.

 

[Hib Halverson]

Have you thought of getting a block off plate and a chip that is set not to show the Code 32?

You have to do more than just change the calibration to disable DTC32. You also have to redo the spark tables because, at part throttle, engines originally calibrated for EGR, will detonate with out it.

Also, in most states with exhaust emissions tests, the lack of EGR on an engine originally equipped with it, will cause failure even before the car's tailpipe emissions are tested.

 

[boomdriver]

Yep...Hib is 100% right on that. The smog test visual inspection not only has a "fail" if any equipment is removed or altered but you will also get tagged as a "gross-polluter" which means a ONE-TIME shot at getting things corrected, or never see a registration sticker again...Ca Has to ability to take your car off the road if you alter the smog equip.
For many of us that meant having to un-do a lot of mods, get smogged, then build the motor back.
Ca is very tough on their smog certs with a 2 yr cycle and then they will throw a random in there once in a while. Any title transfer also requires a new smog. I've had to do 2 in the same yr, or one every year.; No breaks with the SCAQMB.

I've tried to tell people for many years that the avg street L-98 needed the EGR system if they wanted to keep their pistons in one piece...but everybody wants to think 1960 and believe that EGR is the devil. It's not. It's fairly harmless to performance and will help save the motor from knocking itself to death when under a sustained heavy load. between EGR and ESC the engine can use max advance and get the most from its design potential.