rough idle.. sigh
 

OK guys and gals.. HELP!

I have a 91NA.. It runs great, 95k miles.. But when the car warms up, it idles rough.. The idle is steady, just rough.. It sounds like it's missing..

The plugs are new and the wires are newer..

Anyone have any ideas where I start?

Thanks
Dan

is the idle rough as it warms up, or after it reaches normal operating temp? you might want to check the timing on the car. not sure if a '91 n/a is the same as a '90 TII, but i had a rough idle and it was a timing problem. check the crank angle sensor on the front drivers side (right by the pulleys). my car was all the way retarded (i think) so it was misfiring all the time, and performed horrible on the low to mid range.

Do a normal tune up. If the plugs are over 10k miles old, replace them. Do the fuel filter and run some fuel system treatment through it.

Does it sound like it's "popping" and sputtering a bit? If so methinks your TPS may be a tad out of adjustment. The car should idle smooth and steady, with no surging or popping in the exhaust. The TPS has to be set perfectly to avoid either.

It idles rough after it's warm..
And to be honest, the thing seems really slugish on the low-end..

How would I check a rotary's timing?
(I'm an oldschool motorhead, but with pistons..)

Thanks for all your help guys
Dan

btw- yeah it sounds like it's sputtering and popping..

Timing? Until someone comes along with a description you might download the factory service manual at this site http://www.iluvmyrx7.com/Technical_I...nical_info.htm and you'll find a section on the timing. Its a free download. Just download the section you want if you want to save time.

Well it isnt the timing..
I just checked leading and trailing, and they're spec on

Could it be a bad fuel injector?
I've found that it's the front rotor that's misfiring.
Any ideas?

bump

anyone?
heeeelp

3 sensors will basically effect idle after full warmup

#1 and #2 - intake air sensors.. one on the throttle body and one in the afm.. but these rarely go bad

#3 - water thermo sensor .. behind the coolant filler neck, under the alternator.. If this is your culprit, chances are it's sending a signal to the ecu that your coolant temp is still low and so the ecu will keep the car running rich.. overly rich can cause poor/rough idle and the sputtering sound you are talking about.. an overly rich mixture will also make your power quite soggy feeling..

First I've never worked on a 91 and do not know if your car has the same acv that my 87's do but.......the recently rebuilt 87 turbo had a rough, similar to a v8 with cam, idle and I traced it to the acv. One of the nipples on the acv is for the switching diaphram in the acv and that diaphram is cooked and will not hold a vacuum so when at idle when the switching solenoid puts a vacuum on the acv, it was like air leak or vacuum leak. The non turbo 87 also have two pipes on top of the acv that should hold a vacuum. One switching the other relief. Just mentioned this because it happen recently. Yours could be some other thing. I've got three acv for turbo 87's and each one has a baked brittle switching diaphram in them. Anyone else out there with turbo with similar situation? Also I remember someone who traced a rough idle to the diaphram in the egr valve being broken, baked etc. Leaked air when should have been pulling a vacuum. Not saying that this is Your problem, but worth looking into if the other posts don't pan out.

Chris NG:

Thats a possibility.. I've also noticed my gas mileage has gone to heck, so an overly-rich condition is definately possible.

Also my exhaust smells worse than normal, but without a cat, I thought it was normal, now I'm not so sure..

It's POURING down rain here, so when it lets up I'll head outside and check it out..

Do you have to pull the alternator to get to it? or is it visible from up top?

Thanks for all your help guys!!

Dan

Before you buy anything make sure the water thermovalve is opening all the way when the car is warm.

For some reason my thermovalve isn't getting enough hot water, and doesn't open up all the way. To band-aid this problem I took the spring off the fast idle cam and wired it back with a twist tie, now the thermovalve no longer affects idle.

Basically the thermovalve is a themostat. Coolant runs to it, and once the coolant has reached a certain temperature it opens. When it opens it pushed down on the fast idle cam. The roller that touched the cam then adjusts the idle to a warm idle condition. See above for my fix.

When adjusting the TPS I strongly recommend you disconnect this thing, because if it's malfunctioning there's no way in Hell you'll get a good TPS adjustment and you're idle will always be shitty.

I plan on actually fixing the problem, and hooking the system back up. But I need to remove the intake manifolds to find where the coolant is getting blocked. I've been lazy so I just disabled it.

Keep in mind that this does not affect how rich or lean your car will run, all it does is adjust idle speed depending on how warm the coolant is. It is not a sensor, just a thermostat.

dont forget
 

intake air leak. Mine does the same thing.g

The thermosensor is a bit of a pain in the ass to remove with the upper intake manifold and alternator in place, but it can be done.. I belive it's a 19mm head size... just make sure your car is completely cooled off when you remove it and have some extra coolant handy to top things off when you are done testing it..

ok.. I changed the thermoswitch, no change..
Anyone have any other ideas?

And I really paid attention today when warming it up, it seems to run rough/misses when warming up too..

Could this be a symptom of low compression? :(

Help!

Dan

Ok I STILL havent figured this one out..

Anyone else have any ideas?

TPS outta adjustment?

i'm not sure if the O2 sensor would affect this rich lean mix at idle? how bad is the gas mileage?

have you checked the codes? what ones did u get? crank angle sensor?

no codes, and I have a new/used crank angle sensor on the way.


btw- new O2 sensor.. and I havent checked gas mileage per sa, but it's gettin worse mileage than my 87na with bad oil seals and 146k miles..


so I dunno.

I've been looking around, and am thinking is the crank angle sensor doesnt work, I'm gonna rip the top of the intake off and clean the fuel injectors and see if that helps.. I dunno what else to do.

and to top it ALL off, I'm having problems with my brakes!!
All of a sudden, It's getting harder and harder to stop.. kinda like my pedal is getting harder...
ugh..
shoot me..


Help!

rough idle.. sigh
 

I think you discovered your own problem. You said the brake pedal is getting harder and harder. Your brake booster diaphram could be leaking vacuum, causing rought idle because of lean mixture and misfire. Try plugging off your brake booster vacuum hose and see if it smooths out.

well I changed the crank angle sensor today, no chance..

And I tried to pull the brake booster hose off, but that little sucker won't budge..

any other ideas?

ok.. now it's to the point when it runs rough at any speed, not just idle..

HELP!

anyone?
Please?

this will sound funny, but i had an idle problem and the car was running extremely rich; found out the trailing plug wire were reversed. i was outta country and had someone do a tune up before i got back. he replaced the wires to were the coils were labled, but the coil was labled wrong. something simple causing a lot of grief.

Seems RXFORFUN has a good point. Equivalent of a vacuum leak. Heck, is a vacuum leak. Pull the hose off and plug it and run the car. If its hard to get off, well just auger in and get it off.
Could be low compression too. You hint at it. I'd check the compression before I bought any more parts. Just get a compression gauge and pull the valve stem out of it. Pull the plug off the crank angle sensor, car in neutral,compression gauge screwed in one of the top holes, lower plugs out, crank the thing over with very fresh battery and look at the needle bounce. Up and down up and down. Look for the needle to bounce and equal amount each time it travels up the scale. Both rotors need to be close to each other or the car will idle erratic.
I think RXRORFUN could be on to something.

I would say it's a vacuum problem, especially if the brakes pedal feels harder to push this would meen low vacuum, wether it's the brake booster or not you will have to prove it. If you can not get the line off, than pinch it off with a vise grip and see if the idle smooths out. Do you have a vacuum gauge? Have you done a vacuum check with carb cleaner or something similar? This will prove there are no external leaks. Could still have internal leaks in the ACV. Anybody know what he should have for a vacuum reading at idle?