Odd idle surges/dips at cruising speed on 2000 GT & AC Idle surge issue

heffe2001 · May 28, 2014

Just noticed on my way home today an odd drag feeling on my 2000 GT. There was no AC on at the time. I would be cruising around 70-71ish, and around 2200-2300 rpm, and the RPMs would dip down to about 2100 for a second or 2 (you could feel the car slightly slow down), then jump up to 2500 or so for a second or 2, then steady back down around 2200. It did this (that I noticed) about 10-12 times (I have a few of them logged with dashcommand and a bluetooth OBD module, but not sure the PIDS I had set would really help much).

I'm not sure if it's related or not, but I'm having an issue with my AC making idle surge up and down (and you CAN feel it if it's on and at a cruising speed as well), but the AC was completely off, windows down at the time it happened. (AC acts like this video when it happens, not my video, but same symptom: https://www.youtube.com/watch?v=nInBlmrO4CU). I also have a slight leak on the hydroboost module, and it might need a tiny bit of fluid in the steering system due to that.

We're going to work on the AC issue Friday, check the freon level (it blows damn cold when it's running though), and the high/low pressure sensors (low pressure was the guys problem in the video).

Could the AC be kicking in even though it's turned off, dragging down the RPMS for a few seconds, then cutting off? Or anybody got any ideas as to what could be causing it?

My dashcommand exports ScanXL compatible logs (I also have a Diablo Predator I can log with, just not 100% sure how to get 'em off the device, lol), and if anybody can tell me what pids I need to monitor I can get a log of either or both problems..

The car has about 170k on it, I've replaced the IAC with a new motocraft one, changed out all the COPS recently, done plugs recently, cleaned the MAF about a month ago (when I replaced the cheap CAI I had on it with a better K&N). Also replaced about half of the hose to the evap system (need to finish the rest of it, just haven't had a chance to get it on a lift).

heffe2001 · Jun 4, 2014

We replaced the low pressure switch, and made sure to get the freon levels right (tried to replace the switch night before last, and the rubber o-ring fell to pieces, nobody had a replacement that I could find till the next morning, and the valve was slowly leaking, so had to replace all the freon too, lol). Seems to have fixed my surging idle at a stop, and I haven't noticed the RPM dip/surge at cruising speed either.

Is there any way that switch being bad could have caused the idle issues when cruising, even if the AC controls were set specifically to off?

heffe2001 · Jun 18, 2014

This issue appears to have come back again. I also starting having misfires today (not on my way into work, but after sitting since 9 till lunch time, misfiring consistantly every time it's started). Haven't had a chance to see if any cops are wet yet (that's 99% of the time my problem). Also got a P1125 code pending, so I went ahead and replaced the TPS with a new one earlier. Haven't driven it much since then, but will clear the codes and see if it comes back on my way home.

With the driving I did at lunch, I'd have expected to get a misfire code thrown. Haven't seen one yet, but hopefully on the way home. With all the issues I've had the past month, I'm pretty frustrated with this particular car at the moment. Hopefully I can get it all squared away soon, otherwise I'll be in the market for another one in better shape... (If I'd have waited till this year to do my trade, I could have had a '07 GT 'vert instead of the '00, would have cost me a bit, but the 07 was in great shape...).

heffe2001 · Jun 18, 2014

Ok, the P1125 is fixed, as is the misfire (it was cyl 2, there was water down there on that side this time, the plug had a few small divits on the cop-side where the socket catches it from arching on the cop, and the cop boot was malformed). I guess on a OEM/Factory hood, the heat shield kind of redirects any water that may come through the scoop area to the sides, but my aftermarket OEM-style hood doesn't have, that, so if it does happen to leak it goes straight into cyl 2 and 6's wells, which has caused the misfires in the past (I really thought I had that leaking fixed, it holds water in the scoop area when I park in my driveway and it rains, doesn't drain out). The TPS also seems to have fixed my crazy idle problem (knock on wood anyway), as I was able to run the AC all the way home today without any idle surging, which hasn't been the case up to now.

**EDIT** So far, so good, been 2 days now, without any of the aforementioned problems. Tried fixing my alternator whine on my radio today, just made it worse though, lol. Could it be my cores on the alternator causing the issue??