Big RPM drop when clutching with A/C on?

[AviSalem]

So this is a little strange to me. When driving my 99 boxster without my air conditioner on, car drives great, press the clutch and put in neutral, and RPM goes down to just below the 800 Mark and is steady. With the A/C on, in any gear I'm in, and I press the clutch and hold (coming to a stop), the RPMs drop to around 400 rises back up to about 800 and begins hunting before the idle goes back to normal at just below 800 RPMs. Reading up wherever I could, it's sounds like a vacuum leak, but wouldn't that affect the car both when the A/C is on and when it is off? Also worth noting that when shifting gears with the A/C on, I have to give some gas as I'm clutching just so that when I release the clutch for the next gear, my RPMs are high enough. Essentially the RPMs are dropping way to quickly with the A/C on.

 

 

Any help is appreciated, thanks.

Avi

Edited June 25, 2017 by AviSalem

[JFP in PA]

You haven't mentioned any codes being thrown, so I will assume there are none.  The DME is supposed to respond to the activation of the compressor by telling the engine to increase RPM and ignition timing slightly to compensate for the additional load created, making the process rather seamless.  One suggestion I might offer is to check your car's MAF values to see if they are inline with specs.  You might also try pulling the MAF sensor and cleaning it using a quality aerosol MAF cleaner to see if that makes the MAF more responsive.

[AviSalem]

11 minutes ago, JFP in PA said:

You haven't mentioned any codes being thrown, so I will assume there are none.  The DME is supposed to respond to the activation of the compressor by telling the engine to increase RPM and ignition timing slightly to compensate for the additional load created, making the process rather seamless.  One suggestion I might offer is to check your car's MAF values to see if they are inline with specs.  You might also try pulling the MAF sensor and cleaning it using a quality aerosol MAF cleaner to see if that makes the MAF more responsive.

Thanks JFP. I will have to check the codes in the AM, but I know they relate to both banks running lean. I probably should've added that in my initial post! I have already pulled the MAF and sprayed it with cleaner, as well as cleaned the throttle body and IAC. The car has been running this way since I bought it though. I have The durametric, what values should I be looking at? Also, this doesn't occur during idle, I can clutch at a red light with no issues, it only occurs switching between gears.

 

Thanks!

Edited June 25, 2017 by AviSalem

[Ahsai]

Sounds like the a/c is loading the engine more than expected. Have you (a shop) tried vacuuming and refilling the a/c? Any chance of overcharged a/c?

[JFP in PA]

12 hours ago, AviSalem said:

Thanks JFP. I will have to check the codes in the AM, but I know they relate to both banks running lean. I probably should've added that in my initial post! I have already pulled the MAF and sprayed it with cleaner, as well as cleaned the throttle body and IAC. The car has been running this way since I bought it though. I have The durametric, what values should I be looking at? Also, this doesn't occur during idle, I can clutch at a red light with no issues, it only occurs switching between gears.

 

Thanks!

 

If you have a lean condition, I would be looking at the fuel trim values.  The car should not be running lean, usually the result of a small vacuum leak somewhere in the intake system.

[AviSalem]

3 hours ago, JFP in PA said:

 

If you have a lean condition, I would be looking at the fuel trim values.  The car should not be running lean, usually the result of a small vacuum leak somewhere in the intake system.

Hi JFP,

 

I don't think the Durametric offers the trim values for the 986, I just looked through all the options and couldn't find it. Is there anything else I can check? Also, I find it so strange that I can rev the engine in neutral with the air conditioner on and not have a problem, but when driving and shifting gears, I have a problem. I would think if the A/C is pulling too much load, I would have the same issue when I rev the engine and release the gas in neutral.

 

Thanks

[JFP in PA]

It does, should be in the engine actual values sub menu.   The car should not be running lean.

[Ahsai]

Like John said above and look for FRA and TRA (or RKAT).

[AviSalem]

14 minutes ago, Ahsai said:

Like John said above and look for FRA and TRA (or RKAT).

I actually looked at FRA and TRA, sorry for the confusion. One was at .94 and the other was at .37, looked like the 2 banks had different numbers

[Ahsai]

TRA=+0.37 (adding 37% more fuel at idle) means the engine is pegged at full lean on that bank. What's the TRA on the other bank?

Vacuum leak like John said.

 

FRA close to 1.0 is fine.

[AviSalem]

On 6/25/2017 at 8:12 PM, Ahsai said:

TRA=+0.37 (adding 37% more fuel at idle) means the engine is pegged at full lean on that bank. What's the TRA on the other bank?

Vacuum leak like John said.

 

FRA close to 1.0 is fine.

Hey guys, 

 

FRA is .99

FRA 2 is 1.00

TRA is .37

Tra 2 is .37

Load signal is 1.15

Air mass varies from 15.75 to 16.25

[Ahsai]

TRA at .37 but FRA looks great means that you have a large intake air leak, somewhere common to both banks.

Typical places of air leak: oil filler tube cracked, rubber air intake to throttle body not seated well, vacuum leak (vacuum hoses), the elbow on the left intake manifold that connects to the brake vacuum line.

[AviSalem]

Thanks Ahsai, I hope I can find the leak, I don't have a smoke tester. I do use a vape, maybe a couple of puffs to the engine bay will help 

[AviSalem]

On 6/27/2017 at 0:51 PM, Ahsai said:

TRA at .37 but FRA looks great means that you have a large intake air leak, somewhere common to both banks.

Typical places of air leak: oil filler tube cracked, rubber air intake to throttle body not seated well, vacuum leak (vacuum hoses), the elbow on the left intake manifold that connects to the brake vacuum line.

Hey Ahsai,

 

Last night I blew smoke into the J tube coming from the AOS to the throttle body, did not detect and smoke coming out anywhere, even manually turned the butterfly on the throttle to see if I could get anything coming out from that end. Also blew smoke through the J tube the other way, towards the AOS, and still didn't see any leaks. Should my next step be trying to pull the oil filler cap off the car to see how much vacuum it's pulling? On a side note, after reconnecting everything and starting the car, I kept get engine misfire codes with the CEL blinking, needed to clear these out and keep my foot on the gas to keep the car running smooth, eventually it ran ok by itself. The TRA/2 are still running .37.

[JFP in PA]

I would connect a digital manometer to the oil fill opening using an old oil fill cap:

 

 

If the AOS is good, you should read 5 inches of water vacuum level or less.

[Ahsai]

What John suggested above and also check the whole intake path after the MAF sensor for air leak (spray carburetor cleaner on suspected area carefully and have a fire extinguisher close to you). Also check if you have any vacuum hoses disconnected.

Edited June 29, 2017 by Ahsai

[AviSalem]

1 hour ago, Ahsai said:

What John suggested above and also check the whole intake path after the MAF sensor for air leak (spray carburetor cleaner on suspected area carefully and have a fire extinguisher close to you). Also check if you have any vacuum hoses disconnected.

Thanks, I will have to try that when I get another chance, I did pull the oil filler cap with the car running, the idle seemed actually better and smoother with the cap off.

[AviSalem]

Hi All,

 

Sorry for the delayed update. I found a couple hoses broken and disconnected, I used the carb cleaner technique to find my vacuum leak. I am still having the same issue with the A/C on. I also have codes P0455, P1124, and P1126. I have seen many posts relating to P0455 and what can cause it, but I haven't found a write up on how to test the various components. Any help is appreciated.

 

 

Thanks

Avi Salem 

[Ahsai]

Have you checked your gas gap's o-ring and see if there are cracks? After you fixed all the vacuum leak that you could find, you may want to reset the DME and drive the car again and see what codes come back and if the TRA values have improved. All the fuel trims will be reset to 0 so you will need to drive your car for a day or so for the DME to readapt and then the fuel trims will be more of less accurate.

[Ahsai]

Also did you power the IAC with a 9v battery intermittently to make its rotor turn when you cleaned it?

[AviSalem]

7 minutes ago, Ahsai said:

Have you checked your gas gap's o-ring and see if there are cracks? After you fixed all the vacuum leak that you could find, you may want to reset the DME and drive the car again and see what codes come back and if the TRA values have improved. All the fuel trims will be reset to 0 so you will need to drive your car for a day or so for the DME to readapt and then the fuel trims will be more of less accurate.

The gas cap was the first thing I tried, made no difference even with a new one. Also I completed this fix a couple of weeks ago, and checked the values. They are all within 3-4 of being perfect.

[AviSalem]

6 minutes ago, Ahsai said:

Also did you power the IAC with a 9v battery intermittently to make its rotor turn when you cleaned it?

This I have not tried yet after cleaning!

[Ahsai]

Did you reset the DME and do you currently have P0455, P1124, and P1126?

 

P1124 and P1126 are triggered by engine running too lean (intake air leak) or low fuel pressure/flow. If the FRA values (fuel trim under load) are fine, TRA points to air leak.

Edited August 4, 2017 by Ahsai

[AviSalem]

I cleared the codes and had the battery unplugged a while during a window regulator replacement, does that quality as a reset? I will get the values shortly...

[AviSalem]

17 minutes ago, Ahsai said:

Did you reset the DME and do you currently have P0455, P1124, and P1126?

 

P1124 and P1126 are triggered by engine running too lean (intake air leak) or low fuel pressure/flow. If the FRA values (fuel trim under load) are fine, TRA points to air leak.

Yes I currently have P0455 and P1126, P1124 was pending.