Well let me start out by saying that my car will not idle at all. I have some datamaster files that show my map sensor will not go below 74 KPa. Alvin at pcmforless told me the numbers should be like 50-60 at idle and even more with foot on the gas like I have to do to keep it running. The drivers side O2 goes to 9XX mV range and stays there. Passenger side is in the 450 mV range. It keeps fouling the plugs on the drivers side of the motor. Now I have checked for vaccum leaks with carb cleaner around all the vaccum line and intake, made sure 3 times the rockers are adjusted right, and put a new GM MAP sensor and IAC module on the car. Opti is also new if it matters to anyone.

Could this be a bad intake gasket on the drivers side of the motor? Anything else anyone can think of? Extra air is getting in somewhere, but I dont know where. Also EGR and AIR are removed and the EGR is blocked off with plates from steve.

 

Are you sure it's a vacuum leak? A poorly running engine will show low vac. because it can't pull a vac. like a strong engine. Typically a vac. leak will show lean O2's and a higher idle. Check your IAC counts, if they are low then it's a sign of a vac. leak. How is your off idle performance? If it's good then maybe you have a leaky injector thats fouling your 02. You would need to do a cyl. balance test or check your fuel pres. leak down after the engine is shut off. If you still are thinking vac. leak, it could be an internal intake vac. leak. Pull your oil filler cap, if your idle fluctuates then it may be a blown intake gasket below the intake. Do you have any codes? How's your fuel pressure? Maybe a leaking pres. regulator. Good luck.

 

I have tried two different sets of injectors with the same results. Also the AFPR is a brand new aeromotive unit. IAC counts were constantly over 100 until I got a new one, which brought them down to the 90's. Also I cant drive the car while it is like this and it will not hold an idle so I cant check the oil cap idea. I have no ses codes and I actually have the fuel pressure set at 39 with the line off.

The MAP is getting an extra air reading from somewhere though. I did get a high MAP ses light last time I datalogged it. I have since changed the MAP, but it really didnt change anything.

 

Disconnect your map and plug the line to the intake. Put a vac. pump on the map and try pulling it down to 18" - 20". Check your vt on the scanner and see if it's around 1.25 - 1.5v. This will check to see if your map can read correctly. Also check your engine vac. with the gauge and see if it correlates with what your map reading is on the scanner. If you can control your map with a vac. gauge the pcm should start to pull fuel because it thinks this is the actual manifold vacuum and hopefully smooth out the idle a bit or at least cause it to run lean if there is a vac. leak. If it doesn't then look elsewhere, your map is only reacting to something else causing your driveability problem. If you can't pull your map vt down with the vac. pump then check your vt to it and the ground. A poor ground will cause faulty readings to the pcm and cause it to run rich. You should read 5v on one wire, another will read continuity to grd, less than 2 ohms should be ok and the other wire will read a feedback vt to the pcm. I'm not sure which wires are which but with the con. disconnected only one will have vt and the one on the other side of the con. should be grd. Typically the center wire is the signal wire to the pcm. Post your vt readings and manifold vac. readings if you get a chance. I have a cross reference chart I would have to dig out to see if it is reading correctly. Good luck

 

If your IAC counts are ~90, it is sensing too much fuel, not too much air and trying to let more air in.

If your O2s are pegged, then you might even have a problem there.

What happens in open loop?

 

shoebox when the car goes into open loop it will stutter and die with in 30 seconds. Also if it is sensing to much fuel is the MAP sensor trying to compensate for the fuel by pulling more air in?

kjlvilla: what do you mean by vt- voltage or something else.

O2's were replaced yesterday so I will see this weekend if that helps. thanks for the replies and keep them coming.

 

Just to be sure we are on the same page, because your wording "goes into open loop" makes me suspicious- it is in open loop when you first start it, until it is warmed up a bit (just generally speaking).

Are you really saying that it has problems after it goes into closed loop?

 

It runs bad in either closed loop or open loop, but when it goes into closed loop it dies with in the 30 seconds. Sorry I was at school and was trying to do two things at once.

 

Vt = voltage, v = volts. You can check the operation of your map sensor with the key on, engine off. The map is only reacting to the change in pressure put on it, it doesn't need to see the engine running. With the key on, engine off, it should read approx. 4.5v. Maybe a little higher. It should read the same as the BARO sensor on your scanner. Put a vac. pump on it and draw it into a vacuum, the voltage should decrease as you pull a vacuum. Almost all of the sensors on the engine can be checked with a DVOM to test them, you just need to know how they work. I still don't think you have a vac. leak because your engine is running rich. It should run lean because the PCM sees no TPS increase, it should limit fuel. What is your TPS reading? Should be about .40v - .50v with no throttle. A bad TPS can cause a rich condition because the PCM will add fuel thinking the throttle is open if it reads high. Remember, your PCM is a big volt meter, it takes the voltage it sees from sensors and runs it against a preprogramed chart and adds or subtracts fuel from there. If it doesn't see a sensor out of range it will not set a code. You need to check the operation of the major sensors is uses, TPS, MAP, and CTS. If your engine uses a MAF, it will use this also. If you have a service manual, check in the front of the 6E section for typical Tech 1 or Tech 2 scan data, this is a good resource for sensor readings. Also, a poor ground will cause all of your sensors to read higher than they should because the vt drop across the sensor will be skewed higher. This is because the PCM is checking the feedback vt before the sensor ground. If the sensor ground has high resistance, the vt drop across the sensor will be lower, resulting in a higher feedback voltage (Ohms law on series vt drop). I don't want to get too deep into theory here, it's best to verify which sensors are working correctly, this will narrow down your search for the problem area. Sorry so wordy, Good luck!!!

 

First off thanks for everyones help.
Now I have checked the TPS voltage 2 times they were both with in specs. I also with engine off key on moved the tb blades to full throttle to check for any surges of power or loss of power and it was good.

What is a CTS? I have a 93 LT1 GM service manual and will look at chapter 6E. Also motor is a 93 so no MAF, just FYI.

Does anyone think this is a computer problem? I had an alternator go bad and it was charging over 20 volts. The gauge was not hooked up so I dont know how many times the engine was started like that. The problem seemed to get really bad after that happened. Could be unrelated but thought I would ask.

 

Okay I know what the CTS is now, and I have an update. I changed the computr today and unhooked the brake booster leavig the barb fitting on the intake open. The car fired right up and would idle at 1500-2000. When I would put my finger close to the fitting the car would sputter and die. What does this sound like to you guys? I have no idea, and will get another datamaster run on the car soon to check out some numbers.

 

It should actually die if that large vacuum port is left open. Maybe your IAC is stuck closed or the passage is clogged, not letting in any air. Sounds like you are getting way too much fuel for the a/f ratio.

How about something as simple as an obstruction in the intake plumbing? You didn't leave a rag in there, did you? Since you have a 93 and no MAF, have you tried running it with the intake elbow totally off (or at least open on the filter side)?

 

Yes we have tied letting it run without the filter on it and without an intake at all. No difference. The IAC is a brand new GM part, less than 1 week old. Should I turn the Fuel pressure down? Would that make a difference?

 

Your earlier statement of pressure at 39 should not be a factor. Try resetting the IAC with this procedure:

-Depress accelerator slightly

-Start engine, then release accelerator pedal, run engine for 5 seconds

-Turn ignition "OFF" for ten seconds

-Restart engine and check for proper idle operation

 

You posted that you had a vacuum leak,well mine did to this week,the dealer said the last person who installed the map sensor forgot to put int the rubber gasket(grommet) that goes in there as well.It must be air tight.Hope this helps.Seems the wires on these 93 are toast after ten years.They replaced the green connector as well.My02(They also replaced all the wires leading to the idle control valve to).