HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Hunting Idle With Air Conditioner On

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Hunting Idle With Air Conditioner On

Post  mweinst on Fri Aug 29, 2014 9:56 pm

Hi Everyone,

I have a solid, running car except for one thing. The car idles perfectly with the A/C off, but not with the A/C on. With A/C on, the idle goes from it's normal 800 rpms, down to 450 rpms and bounces cyclicly between the two. This will go on indefinitely or until I turn the A/C off.

I bought the car already built, so my technical knowledge is limited. I know that the PCM can control the A/C and bump up the idle when the compressor clutch engages. However, my car's A/C is independent of the PCM.

I am going to test the IAC this weekend, but I imagine that it's ok since it holds the idle well with the A/C off. Strangely, the throttle position sensor shows a slight opening off the throttle blades with the A/C on. With it off, it shows that the blades are closed. I'm not sure why this is happening.

Hopefully, someone here has dealt with this issue before and can help.

mweinst

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Re: Hunting Idle With Air Conditioner On

Post  948 on Tue Sep 02, 2014 11:48 am

Welcome. Where/who did you purchase your car from?
Does your car still have a stock throttle body? Larger aftermarket units can have issues with base idle setup.
For a stock throttle body the first thing to check, using a program like DataMaster, is the IAC counts. With the engine at operating temp the counts should be 30-35. If the counts are too high then the system could run out of adjustment range when the AC kicks on? Also check the TPS is functioning correctly, which can be checked in DataMaster too.
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Re: Hunting Idle With Air Conditioner On

Post  87-944S on Tue Sep 02, 2014 4:14 pm

Does the LT PCM have an A/C select input pin like the LS? I applied a signal from the Porsche A/C system (I think +12v) to that pin when the A/C was turned on so the LS PCM could adjust engine parameters, worked like a champ.
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Re: Hunting Idle With Air Conditioner On

Post  mweinst on Wed Sep 03, 2014 1:11 pm

I bought the car from Al (sbwrench). It's a great car - well put together and a lot of extras.

I cleaned the MAF sensor and the problem cleared up a bit. The idle still fluctuates, but now only between 700 and 950 rpms. I think that I have a couple of bad injectors though. I got an IR thermometer from Harbor Freight and checked each header tube. The front, driver's side tube is about 100 degrees less than the others on that side. My LTerm fuel trim is consistently rich on that side (113). The O2 sensor seems to stay down in the 300 - 400 range on DataMaster.

On the passenger side, the 3rd tube back from the front of the engine is 100 to 150 degrees hotter than the rest on that side. The O2 sensor on that side fluctuates normally, and the LTerm fuel trim is around 125. So, does that indicate that the injectors aren't flowing the same?

I'll have to run a new DataMaster file and recheck the TPS readings.

I don't really know about the A/C thing, though

mweinst

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Re: Hunting Idle With Air Conditioner On

Post  Admin on Wed Sep 03, 2014 7:40 pm

Clean all the injectors and replace the O ring seals while you're at it. The idle problem can be fixed if you will find the AC request wire on the ECU and hook it to the same wire as the compressor, this will let the ECu know when the compressor is on and it'll help control the idle.

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Re: Hunting Idle With Air Conditioner On

Post  mweinst on Thu Sep 04, 2014 8:01 am

Thanks for everyone's input. I will try these things and hopefully that will take care of my issues.

mweinst

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Re: Hunting Idle With Air Conditioner On

Post  948 on Thu Sep 04, 2014 1:59 pm

Al is a great guy, and IIRC you got yourself a great car for a good deal....

As Eric mentioned, hooking up the AC request wire may solve your issues......my car was able to stabilize the idle without the AC request signal though; it has since been hooked up.
Split LTFT could be injectors, O2's, intake leaks around the ports, un-matched heads if they are ported heavily; sending the injectors out for cleaning is a very good starting point.
Did you determine the IAC counts and type of throttle body? Also you may want to consider checking/setting up the base idle.
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Re: Hunting Idle With Air Conditioner On

Post  mweinst on Thu Sep 04, 2014 8:54 pm

Well, I had the injectors cleaned today and they were in bad shape. Now they all flow the same, (much more than the car is tuned for) so I'll have to see what the DataMaster log shows. Of course, when I reinstalled the injectors I managed to crimp a fuel line. It burst when I turned on the fuel pump. I'll get a replacement tomorrow.

I am in the process of getting the car tuned by mail, so I'll have to get that redone to compensate for the injectors, so it may be a few days before I know if this solved my problem. I have a lot of variables going on right now, so I'll update you sometime next week when things get narrowed down a bit.

As far as the throttle body goes, I have a 58mm BBK. My IAC is reading between 55 and 59 at idle.

Thanks for helping me out. I'll take any advice that you can give me!

mweinst

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Re: Hunting Idle With Air Conditioner On

Post  948 on Fri Sep 05, 2014 10:44 am

Okay, once you get a new base tune let us know.
BTW, I have had good luck with base tunes from PCM 4 less.
Also, what size injectors do you have?
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Re: Hunting Idle With Air Conditioner On

Post  mweinst on Fri Sep 05, 2014 12:29 pm

The injectors turned out to be 42# Lucas. Based on the part numbers on the injectors, all of the info posted on the web, and the datalogs, we thought that they were 38#. So, back to the drawing board as far as the tune is concerned.

I had one other car tuned by PCM 4 Less, but this time I went with Solomon at LT1PCMTuning.com. He has supposedly tuned over 1000 LT1's, so I'll see what he can do. If it doesn't work out, PCM 4 Less is my go to backup.

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