FallenCho

iTrader: (1)

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)

Gadd

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.

psquare8

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.

FallenCho

iTrader: (1)

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.

psquare8

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?

DigDug

+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.

FallenCho

iTrader: (1)

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.

psquare8

+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.

FallenCho

iTrader: (1)

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*

FallenCho

iTrader: (1)

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*

moconnor

iTrader: (14)

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.

FallenCho

iTrader: (1)

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.

DigDug

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.

FallenCho

iTrader: (1)

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.

psquare8

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

psquare8

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

FallenCho

iTrader: (1)

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.

FallenCho

iTrader: (1)

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.

DigDug

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

psquare8

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.

Mahjik

iTrader: (1)

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.

FallenCho

iTrader: (1)

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.

Gadd

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.

FallenCho

iTrader: (1)

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.

FallenCho

iTrader: (1)

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?