Rough Idle Need Input
 

I've had this issue for a very long time now and still can't figure it out. When the car is fully warmed up the idle is a little low and rough and if I hit the window switch or apple the brakes while stopped the idle drops and the car runs really rough and the lights dim as well inside the car. However if I turn on the headlights the car runs beautifully with no problems at all. I've checked so many things and I'm at a loss. The only thing left in my head is maybe grounding? Does that sound like a problem bad grounds could cause or a bad alt, bat, starter cable could cause?

Things I've checked:
Alternator (good)
TPS (adjusted)
ISC (good)
Vaccuum lines (all good from what I've checked)

Assuming your car is a five speed, and your plugs are not worn out. It sounds like your idle is set too low or the clutch switch is bad / sticking. You can search "clutch switch" you'll find lots of threads on where to find and how to fix the switch.

To Adjust the idle, bring engine up to normal operating temperature. Jump the TEN and GND in the diagnosis box, adjust idle speed to approx. 750 rpm by turning the idle speed adjusting screw located UNDER the throttle body between the two 10mm cap nuts that attach the elbow to the throttle body. While adjusting idle make sure the fans are not running. Remove the TEN-GND jumper.

Check the check valves. Refer to the FSM for locations- I would start with the one inside the vac hose off the master cylinder as you mention it does it on braking. The hose has a check valve buried inside to allow a one way vac air flow - an idle drop on braking often means this is shot. $22 part kit fdy2-43-480 - It is L shaped and right from the brake master. If the alternator and battery are both solid the idle drops with an electrical pull is odd and could be grounding. Look at the ground wire off the top of the firewall middle to the engine-the black plastic clip is often a source of trouble. TSB 005/97 - March 10, 1997 - Should be able to find it somplace on the forum. It references your problem when the AC comes on - I suspect a power window or other electric system could do it as well. TSB is three steps, check / clean engine harness ground, check / clean main battery ground and replace firewall ground. $12 part fd01-67-e70a(may be a new number today) IMO I would replace these two parts on every FD and clean the grounds on a regular interval - maint items.

Thanks for the suggestions...think I'll make a trip to the Mazda dealer tomorrow and get that new grounding strap which I think they redesigned from what I've read here on the forum. As far as the clutch switch I shall do a search and see what I come up with. Thanks again...this is getting to me bad.

You say it runs better with the lights on. Does it run better with the AC on? Does the idle drop when you turn the AC on and then does it smooth out?

+1 for idle adjustment. Turning on the headlights (or even parking lights), or turning fan to position 3 causes the ECU to raise idle, which is why it's smoothing out when you do that. When the idle is too low, additional electrical loads will cause the idle to drop further and dim the lights. By all means address grounding, but I bet raising idle with the air-adjusting screw will fix the problem.

Yes the AC does cause the idle to dip and go up and smooth out. I also just checked out the clutch switch and it checked out fine. So I shall try the idle out next. Thanks and keep the suggestions coming cause my mind is blank.

+2 for idle adjust given that condition. Given the brake issue look into that check valve if you still have an idle drop on braking. If the idle adjust does not resolve the main issue there are some other possible items to look at.

Well I just got done checking the line that gos from the Master Cylinder to the UIM and if there is suppose to be a check valve in there...there isn't one. Air flows freely both ways as the FSM says it shouldn't. Doesn't make sense to me how this could go missing...I did have my UIM off and practically everything else close by ripped apart before this issue but could the check valve really jsut fall out so easily? *scratches head*

Also if I order this part from Mazda you get the hose and the check valve? Just to make sure you can't just order the check valve seperately or anything. I guess this could explain my spongy brake pedal...*feeling stupid right now*

I would not buy those check valves from Mazda - they will cost you $100+. Search for 'Viton check valves' here to find a much cheaper and better alternative. And I hope by 'Mazda dealer' you mean 'Malloy Mazda' - your local dealer will probably ream you.

Well it's not a regular check valve like the green and white ones...it gos inside the hose literally. So I doubt there is an aftermarket alternative. However I know they will probably rape me cost wise for it :(... the cheapest part I ever paid for from my dealer cost $15 and that was for a e-brake switch.

mazdapartscheap.com has it listed for $16.60 - not too bad.

Is there a valve in the hose at all? You should be able to feel it when you squeeze on the hose. Maybe it got replaced with some plain hose at some point.

Yeah I squeaed the hose and felt nothing and straightened it out as best I could and could see nothing inside. Well it doesn't make sense cause the car ran perfect til I took the UIM off to get some things done and after that the idle has been rough and the brakes have never felt the way they should...lots of play and sponge feel to it but the brakes still work but not how they should.

pn = fdy2 43 480 - this is a common problem as I noted above and no one seems to realize it. $22 part- the ECU can adjust idle for the issue as it raises when lights go on and even more when ac goes on. good luck

I do not think the Viton would work in this location. This is a weird little valve inside the hose - it needs to be in the right place and have the correct flow to not mess up engine vac

I just got back from my dealer and ordered the hose and should be in tomorrow. Only cost $22 so that isn't so bad. Well wish me luck when it comes in and thanks.

Well got the parts in and apparently there is two hoses to that item number and once I saw the second hose in the bag I lost all hope and sure enough my hose is fine. I thought the hose with the check valve was the one that actually connected to the UIM but apparently it's the one before that so now back to depression and square one. So tomorrow I shall try the idle adjustment.

Funny, on my last post, I was about to ask why you would have pulled the hose off the booster when removing the UIM...

If an idle adjust does not do it check the following, compression test, fuel pulsation damper, LIM gasket. I would also install the new vac hoses and see if it improves the brakes. In addition clean up the grounds to eliminate that possibility.

Originally, the check valve was in the UIM side of the brake booster line. However, they had check valve failures due to the heat from the pre-cat and turbos on that side and a TSB move the check valve to the drivers side of that line.

Ok so today I got the TPS tuned in perfectly *gotta love that ground in the diagnosis box* and then I adjusted the idle to 750 on the dot and it holds the idle perfectly however the vacuum on my boost gauge reads 12.5-13'sh on idle and I still have the issue when putting an electrical load on the car besides the air conditioner and headlights obviously. Idle still dips way down when I hold the window switch up or down and the idle tries to regain itself but still is a bit low until I let go of the switches then it is perfectly fine again.

So now I wanna check the grouns so does anyone know the part number for the updated ground cable from the UIM to the firewall? My dealer couldn't find it for the life of him. Thanks again for all the responses.

Did you disable the ISC when you made the idle adjustment? If you did and seeing as the idle vacuum is that low, it's time for a compression check.

If you mean unplugging the Idle Speed Control Valve then no I did not do that. Supposeably my mech did a compression check and said the engine was still running strong but he isn't the smartest person in the world so maybe I'll take it to Mazda and see what the one whole rotary mechanic there says.

Ok since I had just gotten back from eating and my car was warmed up I decided to take your advice and disconnect the ISCV while the car was running then I adjusted the idle air screw to get the idle to 750. I then turned off the car and disconnected the battery and reset the ECU. Plugged the ISCV back in and turn the car on. The idle would stick at 1100RPM unless I hit the window switch which dropped the idle way down and then the idle stuck at 750RPM until I gave it gas then it stuck back at 1100RPM...so maybe a sticky ISCV motor? However that still wont fix my electrical load issue but could the idle sticking be a crappy ISCV or did I do something wrong?

No, I ment by Jumping the TEN and GND in the diagnosis box, before you make the adjustment ( but unpluging it would work too). Then the ICS will have enough range to control the idle properly.

Oh yeah I did jump the TEN and GND since it was mentioned however I did not know why I had to do it but I still did. However I don't think I jumped them correctly cause unplugging the ISCV made a huge drop in the RPM as opposed to the jumping did nothing. *ready to pull his hair out* At least I'm getting things checked off my list so not to many more things to check cept I was thinking of getting a new cable for the battery, alt, and starter and seeing what that does. :-/ Then next two days off I think I'll schedule to get a compression done at Mazda by their elite non-master rotary mechanic.

PN new fd02-67-e70 listed as an Earth wire. Have them pull TSB 005/97. PM your email and I can get you a PSF of it on Monday but I think they are out there. Given what you are describing I doubt its the ground. Get the LIM checked - and if you can find a stock ECU from another car you may try swaping it out to see if the ECU is flukey

do you have a stock ECU?

Thanks for the part number psquare8! Also it is a stock ECU and I still haven't fixed my problem. Some other things my car likes to do especially on a cold night is when I go to turn the car on the key gets to the ACC setting and the electrical power comes on for a split second then shuts off and all electrical power is gone until I pop the hood and wiggle the negative cable on the battery terminal then the power comes back on without have to disconnect the cable..just rotate it. I've cleaned the connections and don't have a clue. So far I've rulled out...

Idle setting
TPS
Battery
Alternator
Most grounds

So now I've been looking through the FSM and was thinking to check the electrical load system box but I have no clue what the FSM is saying in order to inspect it. Frustration is my life. :(

I should also probably mention that my car runs "rough" as in runs like crap and completely changes exhaust sound under around 1800 RPM's the car drives and reacts perfectly above 2k but under it runs pretty choppy. As if the car is running really rich or really lean. The only other thing that comes to mind is that the nipple on the double throttle solenoid broke off and that hole isn't plugged but all the connections on the manifold are plugged and I was told that leaving the solenoid unplugged shoulnd't effect the car. Hmm I think thats pretty much what I got to work with right now.

have you done a compression check?

The brake booster hose has the check valve in the hose, about in the middle of the hose. squeeze and you'll feel it. also you can kinda see the bulge, like a snake with something in his belly. i replaced mine recenty because I was having similar problems, and I thought that might be the culprit. the hose comes with both hoses and it was only like 30 bucks.

well i kind of had the same problem. i did a compression test and it was low and on the way to the dealer to get an engine rebuilt i pulled it a little to hard and broke the apex seals in the front rotor.

So i recomend you get your compression checked i tried fixing the same problem for like 2 months before blowing the seals completly. when my engine died i have 90psi on the rear and 0 on the front rotor

FallenCho,

Did you ever get the compression checked with a rotary checker like you said you were going to?

Dave

I haven't been able to get the compression test done yet thanks to my dealer only having one rotary mech and he's hardly ever there. Gonna try calling again today and see if I can get in. However I don't think it's the compression at all cause the motor pulls hard and runs strong and the only time I had any issues with my car was after I had grounded that throttle cable to the alternator...then my current issues occured and the only thing that I've really found that was bad was the IACV which was replaced. However the compression test can't hurt but 6k for a rebuild if so can make a man cry inside. :(

Well, it's like going in for a physical exam - you don't want to find out anything is wrong, but if you find out you (or in this case, the engine) are in good health, then you don't have to worry about it. And if it's not, then it's better not to waste time trying to fix other things that were not the problem, and concentrate on what is.

Dave

yeah, I think low compression is causing my similar problems. I've got 80k on my reman, so I think it's time.

the reason it runs perfect off idle is because the faster it spins, the more compression it makes. less time for the air/fuel mix to leak out the seals. mine runs like a dream above idle.

LMFAO! My dealer just quoted me 180 to get a compression test done...trying to say it will take 2hrs. Now tell me thats not bs.

not BS to me. I work at a dealership and know what it's like. also, the spark plugs are not the easiest thing to get in and out.

I just changed all four of my plugs in 20 mins this morning...that was without taking off the elbow or any other part and god damn my plugs had more build up on them then anything. Maybe my gas mileage will improve a lil now. :(

well, if you don't like what they quoted you, don't pay it!

Well the buildup could be a variety or reasons. The $160 is a bit high but not much- a good rotary shop is going to charge close to that - call them and ask. Labor rate is probably $80-100/hr. Multiply your 20 time 4-that is 1hr and 20 minutes - they will check Leading and Trailing on both rotors. THey also need to take the elbow off to get some room to work, and disconnect reconnect etc. While they are at it have them check your LIM gasket - if its blown it can do what you are seeing.

I think the build up was from when my turbos went bye bye since the mech who did my turbo install didn't put new plugs in and the engine had flooded. If you guys think that price is right then maybe I'm wrong but I've just looked at it in terms of how fast I can take off the elbow and undo the spark plugs but I guess it's still cheaper then spending 1k on your own compression tester. :-/

However it looks like the compression test is now my last thing to get done since I checked my MAP sensor and finally did my plugs and that all checked out. Also I tried the carb cleaner trick on my LIM and the RPM stayed constant although I know this doesn't always work but time to give in for the compression test. Anyways thanks again for all the input...I really do appreciate all the advice even though I'm still very dizzy after hearing the compression test quote...just seemed so simple in my head. *whiner*

pull your EGI relay off (yellow relay next to your battery, box says EGI MAIN)

You want to have your window open or something so that you can hear your starter. Also, have someone at your exhaust pipe if you can, so they can hear if theres compression.

Turn your car over, and make sure the sound of your car turning over is consistent. it should sound like put put put put put put. if you hear a put put put swoosh swoosh put, then you most likely have a bad apex seal. It will probably be hard to tell, but like i said, the main thing you are looking for is consistency of the sound.

if it sounds consistent, then you should be okay.

Why waste time just go get the comp test done man! it will save you alot of trouble casue that might be the problem.

I haven't got the comp test done cause it's $180 and I seriously don't think my problem has to do with compression because my car ran perfectly fine until I hit that throttle cable to the alt and that killed some sensors which I've replaced and that fixed my surging idle problem and some others. I'm led to believe that this last problem is definetely electrical in nature because if I remember right. When I was running the Power FC my car had no problems...but I'm not 100% sure. However a friend is gonne lend me his compression gauge so I will just do it myself when I have some more time off just to get that possibility out of the way.

did you do the test that i told you to do?

I know back from the dead but I still have this issue and I have done a compression test and all faces still love me. Vacuum is around 14 and some times around 12 after running the car for a bit. The car still pulls very strong it's just at idle it doesn't like me to push the brakes in or hit the window switches. Also the cars idle will not set unless the car is fully warm. It will sit around 1500 til it warms up and that's on a Power FC with the AWS disabled.

I just got done checking the coils today and they all checked out fine as far as the FSM states. So now I've checked the following:

-compression
-TPS
-IACV
-coils
-vacuum lines
-timing
-probably more obvious things I can't remember

So now Ive come to the conclusion that since my turbos seem to be leaking an abnormal amount of oil through the intercooler pipingand eating coolant I figure they are on there way out even though a forum member said they are lowed miled and all that this must be the cause of my problems. I just ask that someone please confirm that bad turbos can cause vacuum problems on our cars.