Hi everyone:

I need help badly here guys My '93 3.0L Aerostar is running very rough at idle. I mean the car is really shaking there.

Strange thing! It starts up cold or hot without any problem. But from a cold start the car would run very smoothly for a few minutes until the engine wrams up, and that's when the shaking starts. If I rev up the engine a little, it smooths out. On the highway it gives decent gas mileage to the tune of 20 mpg. It passed the California smog check without any problem, even though I looked at the report and it did run a little rich.

I cleaned the ubiquitous MAF sensor until it sparkles and no change took place at all. At this point, I'm suspecting the IAC, but doesn't the IAC valve only control the idle speed when the engine is cold? Or does it also do it after the computer kicks in? It has new Autolite plugs and wires, and it idles fine when cold, so I don't think it's an ignition problem. My thinking is that it must be one of those sensor/relay that is used by the engine computer. By the way, it produces no diagnostic code at all and that's the most vexing part of the problem. If it gives me a code, I can at least start changing things and spend some big bucks (just kidding!)

Oh, I also looked at the engine mounts and all vacuum lines, and they are good.

I would appreciate any thought on this.

Thanks, best regards and happy holiday.

 

Mine had a simular problem, I changed the IAC and problem solved.

 

Thank you Jkorreck:

Before I try that, could you tell me if your problem happened only when the engine warmed up or did it happen at all engine temperatures.

Thanks

 

Mine did the same, changed the iac and now it runs ssmooth. Oh yea it run rough in cold or warm. Good luck.

 

Mine happened at all engine temps, as a warning though I don't know if you have an egr valve or not but the iac I bought online from autozone.com had a different shaped housing than the original that may not fit on a car with an egr valve.

 

my van sat for a while and had that problem and now its gotten better but still acts up here and there. its mainly just hard to start when its been cold for a while. so would the iac solve this problem? also for the guy that had the maf cleaned, did your van run lean before you cleaned it out? im having issues with it leaning out durring accell. any other ideas?

 

Hi suprajztwenty:

I only cleaned out the MAF because I thought that was the problem with my rough idle. I did it first since it's free and it's easy Alas, you got what you paid for, and it didn't improve the situation.

Also, as of now, my car is running a little rich and rough, and I'm not sure if it's the IAC or the O2 sensor. Since I'm super cheap, I'll try to convince myself a little more before I fork out the bucks for either an O2 sensor or an IAC.

By the way, autopartsgiant.com has the Motorcraft IAC for about $56. If I need one, that's what I'll go for, a little more expensive, but peace of mind

If your van has been sitting for a while, the battery might have been dead and the "Keep alive memory" was gone. You would need to disconnect the battery for at least 5 minutes to erase it completely, then let the car run for 15 minutes without any electrical loads. Then it'll "learn" all the new parameters again. Any time you change the IAC or any sensors, that's what you'll have to do.

 

Copper,
On cold start up the system runs in a "closed loop" fashion, meaning all the input sensors to the EEC are inoperative. That said, if you are having rough idle before engine warm up you can eliminate faulty sensors and look instead at things like the IAC- which is operative all times along with the MAF. I would tend to agree with some of the previous posters that the problem is more than likely with the IAC valve. After warm up, there are sufficient counterbalances from the various sensors to correct the idle problem. Cold starts are programmed to run rich. It sounds like the IAC is sticking open and giving too lean a mixture for the default injector and timing settings. I'm not sure if this would work, but you could remove the IAC, plug the opening and do a cold start up. If it idles properly then the valve is indeed sticking open.

 

Have you tried checking for vacuum leaks besides just looking at the hoses etc?
I use Carb-Medic spray carb cleaner. You spray it at the intake gaskets etc with the engine idling. If the idle changes when you spray you have a leak.

aeroc when the engine is cold it's "open loop". Closed loop is when the PCM is using the sensor readings. Not to be picky but I just thought I'd point that out

 

Same problem here had a erratic idle hot or cold ,changed out the iac valve solved the idle problem but still ran rough as soon as it warmed up (after 5 min or so the saga continues...Copper disconnect the iac wire leave it connected to the motor when it is running see if there is any difference if there is none theres your problem.Hope this helps worked for me

 

Thanks everyone for your suggestions. Aerocolorado, my problem is the opposite of what you described. The van runs fine when cold, but rough once the engine warmed up.

I checked the engine mounts and they appeared in good shape since I never had an oil leak. The vacuum hoses looked good and I tested them all out with a handheld vacuum pump, so I'm quite sure they are good. I ohm out all the temperature sensors and they are exactly where they should be. Power to the sensors are all there.

I think Racer might have a point about leaks at the intake manifold gaskets. I'll check and see if the bolts came loose. Other than that, I'm going to try disconnecting the IAC and the O2 sensor one at a time and see what the problem is. I'm quite certain it's one of the three.

Thanks again, and I'll keep you updated.

Best regards and Merry Christmas (if it's still allowed here )

 

Racer and Copper, thanks for correcting the discrepancies in the post. Sometimes I feel like I've had a lobotomy when I go back and re-read some of things I post. Makes me wonder where my brain was at the time.

 

That happens to me sometimes when I post early in the morning before breakfast and coffee

 

OK, an update. I checked the bolts on the upper intake manifold. They are tight and properly torqued. I know because I torqued them myself when I rebuilt the engine

I unplugged the IAC before and after the engine warmed up and that promptly killed the engine in both instances, so I guess that rules out the IAC. I got under the van and unplugged the O2 sensor, and lo and behold, the thing actually ran smoother and the check engine light didn't even go on. What's going on here? Stupid me thought that's the problem, so I went ahead and replaced the O2 sensor. Boy! Talk about 45 bucks wasted. It didn't change anything. Well, on the bright side, I now have a perfectly good used O2 sensor I can sell on E-bay for 99 cents with $100 shipping and handling

Well, at least the car is still running and the shaking is tolerable. Sitting inside the car you won't feel it, but once you open and propped up the hood, the lamp on the hood would flicker because of the vibration. I am beginning to regret being too cheap to spend the $70 to send the injectors out for cleaning when I rebuilt the engine, since I'm beginning to suspect those.

Anyway, I give up. As long as it passes the smog check and gives decent mileage, I'll put up with the annoyance

 

This is another one of those "I seem to recall" moments, so I hope Racerguy chimes in to help out. I seem to recall reading somewhere that in the absence of input from certain sensors, the EEC drops back to a default operation mode, similar to what happens when you disconnect the battery for 10 minutes and allow the EEC to reset. It then "learns" your driving style and resets the EEC profile as necessary. I'm wondering if this is what happened you disconnected the O2 sensor - the EEC dropped back its default settings. In default mode, the Check Engine warning light would not come on either. Since this happens after warm up other sensors such as the Air Charge Temperature (ACT) sensor on the intake manifold or the Engine Coolant Temperature (ECT) sensor could be faulty. Both sensor are relatively inexpensive but there are published resistance values you can check them against. I pulled both of mine some time ago and ran a gross function test by hooking the leads to a multimeter and holding a lighted match near (but not directly on) the sensor and watching for a smooth change in resistance values. Just a thought.