I have been driving this car for about 5000 miles after a repair on a major problem with performance. Before the repair it would run poorly all the time after it went into closed loop, At least now I can use the car as a driver. The car runs presently and is used as my go to car for daily errands but it is not 100 percent. Under the load of acceleration it will bog and ping. It is worse with the AC running and much better with the AC off. I recently took a trip to Carlisle, a four hour ride each way. As long as I accelerated slowly it would run well. When I hit the gas too much or accelerate going up a hill it would bog and ping until it hit cruising speed. Once at speed it would run smooth at up to 80 MPH. I drove the car to golf yesterday which was a 40 minute trip both ways. It ran OK with the same symptoms.

It has to be a fuel issue. With these symptoms are there any suggestions?

Thank you!

 

No, it doesn't have to be a fuel issue. Whatever's going wrong, it sounds like it's happening under increased load (i.e cylinder pressure, i.e. torque). For example, it could be a coil slowly dying such that the spark can't jump the plug gap when cylinder pressures rise. If you suspect fuel, though, then the main thing is to put a pressure gauge on it and replicate the symptoms. If the pressure stays good throughout, then I doubt you have a fuel problem. In the absence of any trouble codes it will be time to start data logging again.

 

Thanks Matt,

I ordered a very cheap ICM to give it a try. I will do the pressure gauge test again under load to see results. I will vacuum test again as well under load. Until then I will drive it until it breaks or gives me a definitive symptom!

Thanks,
Rich

 

It could be clogged catalytic converters. Any backfires?
If you changed the knock sensors in the bottom of the engine block, did you torque them to spec? (13 or 14 ft lbs I think).
That could throw your timing off under acceleration.

 

The cats were replaced recently and the knock sensors were torque to 14 lbs.I have moved the car out of the garage because I am having a new water heater installed. It sits outside in the weather and I have ignored it, no wash, no cleaning!. I drive it as often as I can but it is in a time out from the garage. Yesterday I drove it to run an errand. It ran great without the AC on. I accelerated extremely well at every stop light! I decided to engage the ac and give it a try. It still ran well with no hesitation on acceleration. I am starting to believe that this car is possessed in some way. It looks so sad sitting out side the garage but runs great.

I have been driving the car for about 2000 miles since I check the codes. Yesterday after my errand run I ran the codes for the first time in a long time. No codes at all no warning lights on the dash, nothing!

I have been adding injector cleaner for the last several tanks of gas and the car seems to be running much better. All the injectors were checked for ohms and tested good. it may just be a clogged injector which is cleaning up as I drive?

Whatever it is it will be staying out of the garage in timeout and I will drive it until it either breaks or gets so bad I can easily diagnose it.

Thanks,
Rich

 

Worked on the car today. I replaced the ICM with a cheap one. After blowing the ignition system fuse and taking all morning to figure it out I got the same results. The only change was the cheap module threw code 42. I replaced it with the old one and the code went away I am back to square one! I removed the MAP sensor wire and the car runs great!!!!!! That throws the car into open loop and it runs like it should! The map sensor has been replaced and the wires have been checked several times and they are fine. This I know, disconnecting the MAP sensor causes the car to go into open loop. When the car goes into closed loop all the problems begin immediately!

I believe it is a hidden electrical problem in one of the sensor wires. I have checked all the grounds that I know of and cleaned them. All the sensors have been replaced. Unless I am missing one that would cause this problem. The PCM has been replaced with the same results. The O2 sensors and the knock sensors have been replaced. The MAF, TPS, sensor and the EGR valve has been replaced. The small sensors in the air duct have been replaced as well as the water pump temp sensor. Both Cats have been replaced as well as the opti spark, coil , and ICM. I have run the ehack program and there are no obvious problems that show up!

So if I connect the MAP sensor the car runs terrible, if I pull over and disconnect it, the car run great! I am willing to start over with diagnosing this problem. I will keep the MAP sensor disconnected and enjoy the performance. If I could get the check engine light off with the MAP disconnected things would be better. Things will only be great when this mystery is solved. Where should I go form here? I need a good auto electrician!

Thanks,
Rich Harris

 

Posting is helping me think this through. The car presently runs well with the MAP sensor disconnected and the check engine light on. Code 34 comes up. One of the sensors is greatly effecting the performance in closed loop. Running well in open loop eliminates a lot. It is faulty wiring at one of the sensors. It is not the MAP sensor wires I have check that. What would be the next logical sensor that would have the greatest effect on acceleration?

Thanks
Rich Harris

 

I drove the car for seven hours yesterday with the MAP disconnected. It ran great with the sensor disconnected, any speed and instant acceleration. So I am back to figuring out why? Today I will try something simple. I will connect the MAP sensor but remove it from the intake and block it off. See what happens!

RHarris

 

I am concentrating on the MAP sensor and it's signal. The MAP sensor is getting 5 volts and the ground seems good at idle. I tested the signal wire and that is were the problems seems to start. The idle signal is 2.03, a high reading. The voltage goes down on acceleration to 1.34, it should go up. I have tested the map senor with a hand held vacuum and it the voltage goes up as the vacuum rises. A vacuum test of the intake shows 16.5 at idle and a drop to 5 at snap acceleration and a quick rise to 25 as acceleration increases. The map voltage should rise accordingly but it does not, it goes down! Does not make any sense. More testing later to verify these results.

 

After further testing today the MAP sensor operation itself is fine. It gets 5 volts and the signal wire reads 5 volts when the key is turned on. When vacuum is applied it goes down 1 hg for every 5 hg of vacuum applied. The vacuum from the MAP sensor port 16.5 at idle on acceleration going down to 5 on snap acceleration and quickly up to 20 to 25 on wide open throttle. I don't think that is correct? On idle the MAP voltage is at 2.3. this is in line with the 16.5 vacuum reading at the MAP port, it should be lower. On snap acceleration the vacuum reading goes up as it accelerates, I do not think that is correct either. This is were it becomes difficult for me to understand.They say in the FMS that Map sensor should read around 1 to 1.5 volts at idle that would be around 20 hgs of vacuum at the port. Then the FMS says the MAP sensor voltage should go to 4.5 at wide open throttle. That would mean that the vacuum at the MAP port should decrease as the car accelerates. Mine acts the opposite I get the same reading on the MAP sensor port as I do with any other vacuum port! The vacuum would have to go lower at that port on acceleration if I expect to get 4.5 voltage at wide open throttle, mine rises! I believe this to be the problem. Is there a something in the intake that is not allowing the proper signals to the arrive at the PCM

So.....

1. The car runs great with the MAP sensor disconnected. This rules out a lot, opti, ICM, fuel pump etc. tps etc.
2. The MAP sensor signal is not correct on acceleration.

WHY!

Are there any suggestions as to what it could be? I am getting technical but I know there are some really good mechanics out there!

Rich Harris

 

Get a new MAP sensor

 

I have replaced the MAP sensor, no change.

 

An interesting find yesterday. I was trying to find a possible vacuum leak yesterday. I tested vacuum at the intake with a hand held vacuum pump. The intake would not hold any vacuum. I blew air into the intake and herd a hissing sound coming from the throttle body as I should but I identified air coming from the IAC port in the throttle body. That port should be closed? I removed the throttle body and the IAC. IT does not appear that the IAC is seating in the throttle body. It was stuck open and broke off when I tried to move the pindle. Could this be a cause of my problem. If the IAC is not seating it can cause incoming air to by pass the MAP sensor on acceleration so the MAP is getting a false reading. This is a long shot but makes at least some sense? I ordered a new IAC and a gasket kit for the throttle body. I will clean the throttle body and replace the IAC and see what happens.

I have been down many roads with fixing this car. I cannot believe that this would be the problem, it is too simple!!!!!

 

KOEO IAC should park at ~145-160 which is commanded near full open for engine start. Only time it may be fully seated close is if you have a vacuum leak and the ECM/PCM will try to adjust for target idle rpm by closing it.

 

I believe mine IAC was stuck open. I think this allowed a lot of air to by pass the throttle body opening on acceleration. From the open port on the IAC the air passes under the flow of the MAP sensor. This keeps the intake vacuum high which lowers the MAP sensor voltage on acceleration to 1.34. The PCM does not get the signal of acceleration from the MAP (it should be 4. something) . so performance suffers! This is all theory but at least it make sense to me. There is no other explanation that I can think of that would keep intake vacuum high at the MAP sensor port on acceleration? The intake vacuum should be lower at acceleration with the air rushing into the intake!

Thank you,
Rich harris

 

It seems as if the map sensor when bench tested it indicates properly but when connected to the vehicle it is backwards. Can you verify that your map sensor wires from the pcm pins to the sensor is correct? It's odd if this is the problem if the wiring hasn't been messed with but you should still check it. Map wiring at the sensor would appear to be correct but if pinned wrong at pcm then it's possible this might be the issue.

 

The signal wire goes to the PCM, I have check that. It is the middle green wire. I have checked the voltage to the PCM, The black is the ground on the right and the power wire is gray and is to the left. These wires all checked out.

 

Yeah after I typed that idk how that’s even possible if you’re getting correct 5v and ground but I don’t think it’s possible to blip the throttle and have kpas go down. Restriction upstream of the TB could cause that but highly unlikely. If you think your IAC theory is plausible, can you connect map to another vacuum source and retest.

 

Stew,

Thank you for responding! I have tested the MAP with a hand held vacuum pump and the voltage in the MAP sensor responds correctly. The MAP sensor port is very near the throttle body. In theory this is so the air rushing in on acceleration lowers the intake vacuum pressure at that port and consequently raises the voltage output of the MAP to the PCM.. If I used another port the vacuum pressure would go down initially and then rise to 20 or more. The MAP sensor voltage presently does just that, it goes down and intake vacuum stays high. The PCM in response restricts fuel causing a lean situation (performance problem)? I have to figure out why the intake vacuum pressure stays high at the MAP senor port on acceleration. Please keep the responses coming! The new parts should arrive soon and I will test my theory!

Thanks,
Rich Harris

 

Hi Richard, did replacing the IAC solve your problem?