F355 engine run on when A/C active.

Hi Guy's,
I have a 1996 F355GTB 6 spd manual. I recently purchased the car to add to my 360. When I purchased it the air conditioning was not working.

Thanks to this great site I managed to get it all up and running again. The system was empty with leaking valves in front compartment. New valves fitted and system re-gassed and oiled. After a slight electrical issue preventing compressor from engaging (relay). The system works well and blows cold air.

However I have noticed the following and was wondering if this is "normal" on these cars. When the A/C is engaged I hear the click on of the compressor and the revs rise ever so slightly as normal. However when I drive the car with the A/C off it loses speed and revs very quickly when the accelerator peddal is released. But with the A/C on the car does not lose revs as quickly once the accelerator is released. This is only very slight and I'm sure most people wouldn't notice it. Just wondering if this is normal or I have a component somewhere that needs adjustment/replacemet?

BTW this is much more noticeable at slow speeds traveling downhill.

All feedback greatly appreciated.

 

Just to clarify this happens when going down hill in gear or neutral and the same hill I take it or noticable on all hills?

 

Also not sure exactly but this will be more noticable if your original idle is set to low. I do not believe mine is noticable but will check in the next few days.

 

Thanks Taz,
It is also noticeable when driving on the level, but more so going down a hill (probably due to the fact I am expecting engine braking). This is true on any level or downhill road.

Car is in gear "coasting" with foot off accelerator in all senarios.

To give example when A/C is off going downhill I release accelerator and car revs drop instantly to point of noticing engine braking.
When A/C is on going downhill I release accelerator and revs drop slightly but not completely to point of engine braking. It feels like accelerator is still very slightly depressed.

 

Ok thanks. I think it's running normal but I'm no expert. The reason I say that is that if you set your idle up for the extra load an ac puts on the engine and did the same test my bet is that you revs would not drop as fast either and would be more consistent whether the ac was on or off. I am not basing this on my 355 but on the super bikes I used to race. An old trick we used to do for beginners was to set up the idle up on their bikes from let's say 900 to 1100 rpm. On a super bike you could drastically feel the diff on the engine braking and usually gain a second a lap on a 90 second lap. This taught them not to close their throttles so much entering corners and get on the gas sooner.

 

Since you are noticing this it should only be noticable at lower rpms maybe 2000 and below but not from 7500 to 5500.

 

Correct. Not noticeable at all above 3k. Revs drop as per normal A/C on or off.

 

My next question is what the hell are you doing below 6500 rpm anyway Lol

 

LOL!!!

 

Have you tried the battery cut-off switch procedure yet?

 

No thats a good point! I have had the battery connected since before the A/C was not working. I have not reset it since I got it back up and running. Do you think this would work? I suppose its worth a try anyway.

I keep the 355 on my Ctek charger/tender for a week and then move the Ctek over to the 360 for the next week. This means both cars stand for a week at a time and then get the tender connected for the next week. I drive one car each weekend. (I drive the one coming off the tender as that way I know the battery is full and I'm not killing the alternator).

 

The battery cutoff I WRONGLY assumed you had done. I think this will help if you actually have a problem. This is a must according to all the guys I have talked with sorry I missed that and good call cuneo

 

Just curious did it help at all

 

I've been away on business and unable to try. I will do the reset as soon as I get back home and advise.

 

Well I am back home and have done the reset. Let the car do the re-learn as documented. No change at all. Exactly the same as before.

I am now thinking that this is probably normal. Has anyone checked their car to see?

 

Mine did exactly this and the idle control valve was all gummed up. Took 2 minutes to pull it out and clean it. This fixed it for me.

 

Thanks Mark,
That makes perfect sense. I've done a search and found out where it lives and what it looks like (Just under the Y air tubes from airboxes on my 5.2). Don't suppose there is a guide on how to remove and clean it correctly? I assume contact cleaner would be ok to use? I don't want to just rip it off and spray contact cleaner all over the place without knowing exactly what I'm doing. I don't want to damage anything. Fools rush in where Angels fear to tread etc etc........

Also should it rotate easily or with resistance once I remove it?

Input and direction greatly appreciate.

 

It's a round silver metal cylinder just past the MAF sensor. You'll see it. It's obvious how to get it out. I just took it out and the valve inside wouldn't move at all. I sprayed it with brake cleaner and it freed right up.
I'm guessing a lot of 355 engines have this problem.

 

Thanks Mark,
I'll give it a try. If you used brake cleaner the non-residual contact cleaner I have should be ok.

 

Well I've removed the idle valve and cleaned it. It was a little black inside but not really that dirty. It moved freely both before and after cleaning. Reassembled and took car for a run. Unfortunately no change at all. Still exactly the same.

I'm now thinking that this must be how these cars are. Perhaps I'm too picky....

 

My car acts very similarly, with a/c on the rev drop is slightly slower only below 3k rpm. Above that, it is the same. If I put the car in neutral while moving the idle creeps up a bit (1200 vs 900 normally), which I can't quite figure out why unless it's the air being forced into the intakes vs. when stationary.

 

Thanks Pete, that is exactly same as mine. So looks like it's ok and something I'll have to get used to.
Btw my 360 does not exhibit these symptoms. The revs do rise slightly with A/C on but you cannot tell at all when actually driving the car. The 360 decelerates the same A/C on or off. Must be a newer system fitted to 360 compared to 355. Which is to be expected really. It is certainly a more modern set up and cools the cabin much better than 355. This is certainly required in my region.
Thanks to everyone who responded and contributed to this thread. I really appreciate it.

 

Nah your not too picky your just driving at too low of rpm ha ha