'97 Deville, runs rough with A/C on

My '97 Deville runs great except when I have the A/C on.  It idles smooth but while driving it runs rough and feels like it has a bad miss and occasionally backfires.  As I said, with A/C off it runs great and the A/C itself works good and doesn't make any noise.  Does anyone have a clue what this could be?  Thanks.
 
Dave

Hard to figure these things out from a distance but what is happening is that the AC is putting a load on the engine when the compressor cycles on. This load is uncovering a problem. If it feels like a miss and backfires that's what you have imo, a miss. . Do you have a code? I'd go through the standard items for a miss. Being a 1997 do you know if your spark plug wires have ever been changed? If not they probably need to be by now. Spark plugs, when changed last? Then there is the coils if problem still persists. I always suggest fuel and air filters too.

quote:

ORIGINAL: Katzmans Caddy

Hard to figure these things out from a distance but what is happening is that the AC is putting a load on the engine when the compressor cycles on. This load is uncovering a problem. If it feels like a miss and backfires that's what you have imo, a miss. . Do you have a code? I'd go through the standard items for a miss. Being a 1997 do you know if your spark plug wires have ever been changed? If not they probably need to be by now. Spark plugs, when changed last? Then there is the coils if problem still persists. I always suggest fuel and air filters too.

 
Thanks for the reply, good stuff.  Everything you mention (except coils) is fairly new (less than 20K miles).  The other thoughts I have are...dirty injectors, sticky throttle body, crud in the gas tank.  I do not have  a scanner to pull codes, although I do know it needs an O2 sensor because the SES light is on and the scanner I borrowed a year ago said that.  Could the O2 sensor be causing this problem? Seems unlikely to me and it wasn't having this problem until recently.

if you have been driving for a year with the SES light on, then you have no idea how many other codes may have set since the last time you had it scanned.
 
Step 1.
Scan for codes
Step 2.
Repair the obvious problem first then move on to the next issue.

Thanks.  The SES light comes and goes.  Sometimes it is off for a month at a time (I know about the gas cap so that isn't it) but your point is well taken.  I'll get ahold of a scanner and go from there.

Additional info, it seems to occur once the engine is warmed up, not when I first start it up.  Any additional ideas?  Thanks.
 
Dave

something there does not like heat. 
that points to electrical or electronic.

quote:

ORIGINAL: DeFormula

Additional info, it seems to occur once the engine is warmed up, not when I first start it up.  Any additional ideas?  Thanks.

Dave

The engine computer runs in open loop until it warms up. Uses a base program from the TPS CTS and MAF.
When it reaches operating temp it uses feedback from the o2 sensors for fuel control.

So if one of the o2 sensors is bad it could be giving faulty info to the computer and causing it to run like crap when warm(?)

going by  FLCaddytech   either that is it or the O2 sensors are off-line?

quote:

ORIGINAL: FLCaddytech

The engine computer runs in open loop until it warms up. Uses a base program from the TPS CTS and MAF.
When it reaches operating temp it uses feedback from the o2 sensors for fuel control.

quote:

ORIGINAL: FLCaddytech

if you have been driving for a year with the SES light on, then you have no idea how many other codes may have set since the last time you had it scanned.

Step 1.
Scan for codes

 

quote:

I do not have  a scanner to pull codes, although I do know it needs an O2 sensor because the SES light is on and the scanner I borrowed a year ago said that.  Could the O2 sensor be causing this problem?

quote:


Step 2.
Repair the obvious problem first then move on to the next issue.

 
The o2 sensor may or may not be the problem you are now experiencing. I wouldn't diag the running condition at my shop unless you fixed the o2 code first.

OK, here are the codes.  It sounds like I probably need two O2 sensors to start...
 
P0139 - O2 sensor ckt slow response Bank 1, Sensor 2 (also Bank 1, sensor 1 but I forgot to write down the code number)
P0300 - Random / multiple cylinder misfire detected (may have occured because I hooked up the plug wires wrong when I put on a new set a few months ago)
P0135 - O2 sensor heater circuit malfunction Bank 1, Sensor 1
P0141 - O2 sensor heater circuit malfunction Bank 1, Sensor 2
P1139 - Manufacturer controlled fuel and air metering
 
Go for it tech meisters.
 
Bank one is the bank closest to the frt of the car, correct (?), or whichever starts with cykinder one, I haven't looked at it in a while. :)
 
Thanks guys.
 
Dave

You have five codes saying the o2 sensors are a problem.
Unless you had some very weird wiring problem I'd go with 2 new sensors.
 
Bank 1 is the back head. Passenger rear 1 3 5 7

Thanks FLCaddytech.  I agree, I'll put in two new sensors and go from there.  No weird wiring probs that I know of.  This is a very clean unmolested car.  I'll let you know what happens.