Rough Idle in Drive with AC on

[RECRUISER]

Please correct me if I'm wrong but I have been under the assumption that there is a relay or even the ecu itself that idles the engine up automatically when the compressor kicks in?
If this does exist then someone in this forum will be able to point to the culprit. I'll post and wait for a knowledgeable response.

 

[inkpot]

BMorgan, have you ever replaced the A/C tensioner pulley and bearing? The bearings are cheap, like $12. That tensioner is what keep the A/C belt tight. It could be the belt rumbling because it is loose?

 

[Dave 2000]

This is a guess but the best I can offer ATM, a typical ECU rarely has the current capability to run the AC compressor or fan, most would have a relay between the ECU and compressor/fan but, engine speed (advance and idle ect) are within the ECU's capacity.

Anyone on here have a wiring diagram to help this guy?

Regards

Dave

 

[94crusha]

Long time lurker - first post.

94 - 242,000 miles, triple locked. 4th owner and have owned it for 2 years and done lots of PM and other maintenance. I don't drive very far and have put on about 5,000 since purchase. Basically I split my DD with another car.

So the truck has been running well. This weekend I bleed the brakes (motive power bleeder with the Assenmacher Toyota adapter - lot of threads on bleeding but this is the way to go). Not sure when the brake fluid was last changed - but it has been at least since 2012, if not longer. Now brakes are much firmer at that last point of stop and feel that they would really bite in an emergency stop compared to before - I am pleased.

Anyway, get the truck off the jacks, I run around for a while and I am getting the really rough idle when the AC compressor kicks in and Tach goes to 1100-1200. It also happens when I am driving with the AC off right around the same tach levels. Although it is most pronounced when at a stop and with AC on. Feels like the motor is bouncing around.

Any further thoughts or luck on a fix?

As an FYI, over the past couple of years, I have done the following which are hinted at in some of the above posts and some are just general engine bay work: (i) brand new oem rubber air intake; (ii) new AC Delco charcoal air canister and related hoses; (iii) replaced many of the small PCV hoses around the motor; (iv) replace EFI fuse; (v) reset the timing; (vi) new fuel pump relay; (vii) new valve cover gasket and spark plugs; (viii) new Denso radiator 11/10/17- which by the way appears to have sprung a very small leak between top tank and aluminum on DS [pretty disappointed and have ordered OEM toyota rad]; (ix) replaced one of those 2-3 inch disk shaped valves for PCV system but I forget which one.

Thought I had the truck dialed in real nice before this and now, for first time, I am concerned on how to fix something.

Much appreciated.

94crusha

 

[ElCid04]

With the engine running, in gear, and the AC on, the engine runs rough - steady but rough. It's only when it's under load, but I can tell the roughness is there with the AC off just not bad. EVERY once in a while, I'll stop at a light and it isn't rough, but maybe the compressor is cycling - I don't know.

I've replaced the engine mounts - that didn't do it. I did NOT replace the transmission mount so if that's possible... I recently replaced the AC pulley just in case. I'm wondering if it could be the compressor bearing. Does anyone have anything I should consider? This is my 95 with 180k. Otherwise it runs great - steady. In park, it is very smooth. Idle is steady.

Thank you in advance.

So I had this same EXACT problem going on with my 94 recently. I replaced engine and tranny mounts a couple years ago, so ruled those out. In the last month, I replaced the A/C compressor, valves, along with plugs and Dizzy cap. Still had rough idle. I put on a new set of OEM belts, still had rough idle with A/C on, even with new equipment.

Last week I finally figured it out. I didn't have my new belts even close to tight enough. I bought one of those $12 Gates tension gauges that are all the rage right now, and found out I was WAY below spec on tightness. Cranked things tighter, and the rough idle and rumble magically disappeared. For kicks, I also bumped up my timing to around 7*, and it's as smooth as can be now, with or without A/C running. ( I also run 93 octane anyways, as I had my head shaved when I rebuilt for the HG)

Test your belts and tighten them up. If you dont have a gauge, you should only be able to push them down by no more than 1/4".

 

[94crusha]

Thanks much. Just bought the Gates v belt tension tester for ~$12 off Amazon. I'll give this a shot and report back.

 

[ajax1]

Yo

Long time lurker - first post.

94 - 242,000 miles, triple locked. 4th owner and have owned it for 2 years and done lots of PM and other maintenance. I don't drive very far and have put on about 5,000 since purchase. Basically I split my DD with another car.

So the truck has been running well. This weekend I bleed the brakes (motive power bleeder with the Assenmacher Toyota adapter - lot of threads on bleeding but this is the way to go). Not sure when the brake fluid was last changed - but it has been at least since 2012, if not longer. Now brakes are much firmer at that last point of stop and feel that they would really bite in an emergency stop compared to before - I am pleased.

Anyway, get the truck off the jacks, I run around for a while and I am getting the really rough idle when the AC compressor kicks in and Tach goes to 1100-1200. It also happens when I am driving with the AC off right around the same tach levels. Although it is most pronounced when at a stop and with AC on. Feels like the motor is bouncing around.

Any further thoughts or luck on a fix?

As an FYI, over the past couple of years, I have done the following which are hinted at in some of the above posts and some are just general engine bay work: (i) brand new oem rubber air intake; (ii) new AC Delco charcoal air canister and related hoses; (iii) replaced many of the small PCV hoses around the motor; (iv) replace EFI fuse; (v) reset the timing; (vi) new fuel pump relay; (vii) new valve cover gasket and spark plugs; (viii) new Denso radiator 11/10/17- which by the way appears to have sprung a very small leak between top tank and aluminum on DS [pretty disappointed and have ordered OEM toyota rad]; (ix) replaced one of those 2-3 inch disk shaped valves for PCV system but I forget which one.

Thought I had the truck dialed in real nice before this and now, for first time, I am concerned on how to fix something.

Much appreciated.

94crusha

u have a brake booster check valve and hose right there maybe you cracked one or the other

 

[94crusha]

Yo

u have a brake booster check valve and hose right there maybe you cracked one or the other

Ok. I'll check - but why would that cause rough idle?

 

[ajax1]

Ok. I'll check - but why would that cause rough idle?

Vacuum leak

 

[bmorgan]

BMorgan, have you ever replaced the A/C tensioner pulley and bearing? The bearings are cheap, like $12. That tensioner is what keep the A/C belt tight. It could be the belt rumbling because it is loose?

I'm very sorry I'm just now replying. Coincidentally, I did replace that pulley. It didn't help.

I'll get a belt tension tester and report back. Thanks.

 

[Michael Hanson]

Hi, Vacuum leak probably.How long has it been since the valves were adjusted and the valve cover gasket replaced ? Mike

 

[bmorgan]

Hi, Vacuum leak probably.How long has it been since the valves were adjusted and the valve cover gasket replaced ? Mike

I recently checked all the valve gaps and they were all within tolerance (I wasn't going to re-shim them unless they were out of tolerance - wish I could have just adjusted them). I also replaced the valve cover gasket and spark plug gaskets. I've replaced most of the rubber in the past few years, but I'm always willing to go back and check again. I am smart enough to know I don't know everything and I often do make mistakes.

This roughly has been steady for almost 2 years. Maybe I'm wrong, but wouldn't most vacuum leaks degrade over time? I'm thinking, if I don't find it beforehand, once this brutal summer is over, I'll just replace the compressor

 

[COYS]

So I had this same EXACT problem going on with my 94 recently. I replaced engine and tranny mounts a couple years ago, so ruled those out. In the last month, I replaced the A/C compressor, valves, along with plugs and Dizzy cap. Still had rough idle. I put on a new set of OEM belts, still had rough idle with A/C on, even with new equipment.

Last week I finally figured it out. I didn't have my new belts even close to tight enough. I bought one of those $12 Gates tension gauges that are all the rage right now, and found out I was WAY below spec on tightness. Cranked things tighter, and the rough idle and rumble magically disappeared. For kicks, I also bumped up my timing to around 7*, and it's as smooth as can be now, with or without A/C running. ( I also run 93 octane anyways, as I had my head shaved when I rebuilt for the HG)

Test your belts and tighten them up. If you dont have a gauge, you should only be able to push them down by no more than 1/4".

This is great stuff. I posted up about this distinct cabin vibration whenever the AC compressor cycled on and you're the first one to come up with a solution to this annoyance. Thanks!

 

[Jason hansen]

Partially stuck open erg valve?

 

[bmorgan]

Partially stuck open erg valve?

I'll give it look. Thank you!

 

[rolliges]

A visual inspection of the belts AND even the thumb-test are not enough. I had similar A/C related issues and, for another issue, checked belt tension with the Cricket tool (search).

Looked good, felt good too, measured= way too low.

Proper tension= a few issues solved.

 

[toyogi]

Getting similar issue. AC compressor relatively new. Plugs, wires, etc. relatively new. Also noted revs not as high as used to be on cold start up. Following this thread. Please post if you find culprit. Thanks!

 

[bmorgan]

My belts were loose (around 50 per the Krikit), but that didn't solve the issue. But that has me thinking about the crank. This issue was first noticed around the time I did my first front crank seal. That might just be circumstantial, but now I have to check on it.

I torqued it to 300ft/lbs. At that torque, is it possible to have not completely seated?

I still need to check the EGR....

 

[CJF]

Getting similar issue. AC compressor relatively new. Plugs, wires, etc. relatively new. Also noted revs not as high as used to be on cold start up. Following this thread. Please post if you find culprit. Thanks!

Is your idle jumping up (like it should) when the compressor kicks in, or not?

 

[CJF]

Also: bmorgan, I don't see where you ever answered the above question; did I miss it?