Claynoyes

I have an ’88 GXL, which I bought a year and a half ago. It was in good running condition, it ran clean and idled fine. A few months ago I noticed that on a cold morning when started, the idle would oscillate between 1500 and 1700 rpm. If I tapped the gas, the idle would go to 3k for a short while then drop down to normal. After a while the problem got worse. Now what happens is when started the 3k warm up occurs then the idle drops to the 1500-1700 oscillation, if I tap the gas the idle will go up to 3k and stay there until the car is somewhat warm. After about 5 minutes of idling at 3k it will eventually drop down to the 1500 oscillation again. When driving the car w/ the rpm anywhere between 1500-2500, I can feel the oscillation: the car speeds up slightly, then the throttle lets off. When driving at slow speeds, it is extremely difficult to prevent bucking.
I have checked and adjusted the TPS, I have checked the BAC system. I have made the code checker w/ the LEDs and I get no error codes. I recently had the UIM off, so I removed it again and made sure that the gasket was sealed w/ RTV sealant. I can hear a hiss around the right side of the dynamic chamber, but I cannot pinpoint it. When I use a vacuum hose as a stethoscope, it seems that I am just hearing air traveling through the large hose going into the right side of the dynamic chamber. I have sprayed carb cleaner all around my engine bay and I do not notice any change in idle. I have checked the voltage of every ECU pin and all are within spec, except for the AFM at idle. The FSM says it should be between 2.5 and 3.5V at idle, I can’t remember exactly but I believe it read somewhere around 1 volt. If the AFM is malfunctioning, why am I not getting an error code from it? I did some research on the AFM and all of the symptoms of a faulty AFM seem to be much more severe than what my car is doing. The only other thing the ECU showed was out of whack was the intake air temp sensor. The FSM says it should be between 1 and 2V at 176 degrees Fahrenheit. My reading was 3V with my temp gauge showing the car at normal operating temp.
Should I pursue these for the cause of my idle problem? The FSM does not give a way to check the AFM itself. It just says to take it to a dealer, which I’m trying to avoid. I have run out of ideas and have run out of threads to search for a solution in.
Thank you for any help
Clayton

WAYNE88N/A

Sounds like you got a hell of a vac leak somewhere, based solely on the AFM's weird input voltage at the ECU...

Have you checked the UIM to LIM gasket? If there's just a tiny crack between the two, the result will be massive air loss due to the sheer surface area. Could be the hiss you're hearing...

Another area to check would be the LIM to engine gasket mating surface...

The air temp sensor input will be funny, because the dynamic chamber will not be as hot as the engine, due to the air flowing through it...

There is a bench check you can perform on the AFM, and it IS in the FSM...A bunch of resistance readings to perform...

What's the AFM's input at WOT? I've collected several ECU input readings and recorded them on my car over the years if you'd like to compare numbers...

WAYNE88N/A

Scratch what I said above- the AFM's input is inverse (as the door opens, voltage goes down).

I ran out to the car and got my "book"...1 volt at idle (750 rpms) the same voltage I'm getting at a 90 mph cruise (1.1v recorded), so something is screwy...

What's the AFM's input voltage with the key on only?

You said you checked all of the ECU pins- what was the 5vref pin's voltage?

Claynoyes

Today i rechecked the ECU readings, and i came up w/ different readings. I must have screwed up somehow doing yesterday's readings. I found more components that are not to spec, this time i recorded everything. I will try to upload a word document w/ the table of my readings. If the upload works correctly, you will see that the AFMs voltage w/ key at 'on' is 4.0V, at idle it is 1.73V and when i took it for a run, the lowest i saw the meter at was .4V (accelerating w/ WOT).

One of the components which came up w/ different readings was the BAC valve, the ECU reads 1.37V.--On the chart of ECU readings online the BAC valve has a comment saying "engine signal monitor green and red light flash." What does this mean? I noticed this comment attached to the primary injectors as well.

The only other major difference i noticed between the readings was the relief solenoid valve. I measure 11.71V at 'on' when the chart says i should be getting below 2.0V.

As far as vacuum leaks are concerned, hopefully I will be able to take off the dynamic chamber this weekend and throw a new gasket on w/ RTV sealant and see if that changes anything, (i've got a new gasket lying around that might as well be put to work). The gasket i resealed w/ RTV sealant a few weekends ago was the joint right under the fuel rail.

Also on the chart, my 5V ref. is 4.94V. Im going to look into the AFM tests, my Haynes manual didn't give any bench tests, so now i'll double check w/ the online FSM. Thanks again for your help.
Clayton

Claynoyes

2nd attempt to upload the ECU readings chart...

WAYNE88N/A

Everything looks good except for that AFM reading...

Here's what I've got-

key on- 4v
idle (750 rpm)- 3v
cruise at 55 mph- 1.4v
cruise at 75 mph- 1.1v
WOT- .95v

The BAC valve is doing a hell of a duty cycle, unless you have an open in the wiring and the meter is picking up stray voltage. 1.37v, if it's energized, would be something like a 95% duty cycle, which begs the question- was this reading taken during the 3K warmup?

If it's just key on, then something's wrong, I would think...The BAC should be at about system voltage (around 14v) at idle, unless it's having to make up for an ill-adjusted mechanical idle, in which case it might fall to about 8 to 10v ballpark...

Hmm, relief solenoid valve being energized would just exhaust the air pump air overboard, instead of porting it towards the port air and split air chambers. Don't think that would mess with you too much...

Your 5vref is good- it doesn't have to be perfect, because the ECU (like a multimeter on its resistance scale) knows how much voltage it's sending out, therefore knows where to plot the voltage coming in from the sensors...

Claynoyes

When I took the readings, if the chart did not give two readings, one for ign. 'on' and one for idle, I just tested at 'on.' Any readings I took at idle, i made sure to wait until the 3k warmup was done. So I guess somethings wrong... lol

I'll do the bench tests on the AFM and check for a vac leak around that joint next. I have tested resistance on the BAC, and connected jumper wires and heard a click. So where should I start w/ the BAC valve?
Thanks
Clayton

hugues

boy, you did a great job with that word document ...

the BAC voltage is out of whack for sure ... it should be about 11V at idle with no accessories on ...

I assume your idle is set according to the FSM though.

if the input sensors show correct voltage, then I would suspect the ECU or at least the circuit that deals with the BAC in the ECU ...

WAYNE88N/A

Hey there Hugues, don't see ya too much anymore on here...

Why is your BAC down to 11v at idle with no loads? You sure your mechanical idle is set correctly? Mine reads 13v+ with a no-load 750 idle, which means she's just barely "on"...

Claynoyes- leave the meter connected at the BAC input and start the car. Watch the meter as she goes through the warmup routine and settles into a good idle. Now turn some electrical loads on one by one as you record the readings. What do you get?

BTW- Hugues has an awesome link, read up on it...

hugues

Hey Wayne, I see you re still going at it ... troubleshooting and stuff ... that's nice of you I must say.

thanks for the kind words.

I am actually selling my car (87 sport) which can be seen on the site.

About the 11V at idle for the bac with no accessories that I mentioned, it was not meant to be taken as an accurate measurement ... around 13 V is probably a better number ... sorry about the confusion.

For the thread starter, we really need to know if the idle is set properly that is according to the rules and regulation of the FSM.

Hugues-

takahashiRyosukeFC3S

I'm also experiencing a high idle problem roughly around the same rpm 1500-1700 but mine is steady and does not occilate. I'm also experiencing a short to the battery when the ignition is on. any ideas if that might be causing it?

thanks
TR

WAYNE88N/A

Short to the battery when the key is held to start? That's normal, for a split second.

Short to the battery with just the key ON? Another thing entirely...

You're gonna have to isolate it, most easily accomplished by pulling fuses and noting current flow...

Hugues- so you're getting out of the 2nd gen thing?

Claynoyes

Well here is my update...
This weekend I tore the UIM apart, resealed the joint under the fuel injectors, and the joint at the dynamic chamber. While the UIM was off, I cleaned up the ground wires on the engine and tranny. I also noticed that the back of my secondary throttle plates were coated with carbon buildup, as well as my dynamic chamber. I cleaned up what i could, but i didn't get all of it. with the throttle body off the car, i tested the thermowax... it does not work. I am pretty sure that this is the reason why my idle is at 1500 rpm, cause when i finished rebuilding and started her up, the oscillation was gone, so it now idles at 1500. Does a bad thermowax valve throw off BAC readings?

Also, i am looking to replace the thermowax, not remove it altogether. Does anybody have any ideas where I can purchase one? Or does anybody have one for a manual car lying around that is in good enough condition? Im hoping for a cheap fix...

Thanks
Clayton

WAYNE88N/A

Mazdatrix has 'em, if you can't find a good used one...

I don't know about affecting the BAC (I wouldn't think so), but a bad/ stuck thermowax could be causing damn near all of your problems. Good find!

After you get the idle fixed, then we'll start discussing what the BAC is doing, if ya want

Claynoyes

Well, I bought a used thermowax valve, tested and installed it... No change to the idle whatsoever. The thermowax passed its test outside the vehicle but has done nothing for my idle. And ironically when I replaced it, it seems as though i developed an exhaust leak or something because my car sounds like crap now. Before taking out the old one it sounded fine, after starting it up w/ the new one it sounds different... What are the chances of that?

So, I suppose it goes back to discussing my BAC valve... Where do I start? I was also wondering what the alan wrench hole at the end of the BAC valve is. Just curious.

Thank you
Clayton

WAYNE88N/A

That's weird...

Now are we talking about the thermowax valve that has the two (or three) vac hoses attached to it, for the secondary throttle plate system?

Or are we talking about the thermowax valve that pushes the cam off of the throttle linkage as it warms up? I'm guessing this one...

There's no reason it would make your car sound different...

Have you actually watched the thermo valve in action as she warms up, to make sure the linkage is doing what it's supposed to? Using a mirror can help...

I haven't re-read the whole thread, you've got a high idle problem, right?

HAILERS

888888888The only other major difference i noticed between the readings was the relief solenoid valve. I measure 11.71V at 'on' when the chart says i should be getting below 2.0V********************

I'd say your water temp switch is unplugged and or your TPS is set wrong. Your TPS setting is related to whether or not the RELIEF solenoid is getting a ground signal from the ECU, or not.

Let me take a step back. If the engine is fully warmed up, then the voltage should be less than a volt and a half. If the engine is stone cold, it'll read approx 12vdc. Only you know if the engine was hot or cold when you looked

WAYNE88N/A

Umm, Hailers, isn't that 8888888888 supposed to be a ********????????

Claynoyes

Some things I forgot to mention... as Hugues requested, i tested the idle and it reads roughly 750 oscillating. Also when I took my ECU readings, the car was fully warmed up.

As for the different sound... I just happen to be soo lucky that during the exact same time when I am trying to fix my idle, my passenger side muffler completes its rusting straight through the pipe and confuses the hell out of me when I start it back up. Thus i have 1 functioning muffler, one muffler for looks, and a really annoying car...

The thermowax "valve" that i was replacing was the device that has the 2 vacuum hoses connected to it. That was the "valve" that I pulled off the car and heated up w/ water.. etc etc. The housing for it, as I like to call it, I ended up replacing it as well. I adjusted the screw on it that aligns the plate w/ the cam roller as best I could, the picture and text of this adjustment in my Haynes manual wasn't very clear... so I eyeballed it the best I could. I'm going to crossreference it w/ the online FSM and see whats different in a few minutes, just to make sure that the adjustment is fine.

Oh ya, and my issue is a high oscillating idle. Between 1500 and 1700. Another interesting thing, when I start my car cold, it'll rev to 3k and sit ther efor a long time

Claynoyes

... hit wrong button...

and after my car starts to warm up, the idle will drop down a bit and oscillate, and as it gets warmer, the oscillation will slowly recede to 1500rpm. Just some more info...

Again thank you for your help
Clayton

WAYNE88N/A

The 3K thing happens for 17 seconds, which seems like a long time when sitting there in the car. That's a normal "accelerated warmup"...

Is there any change to the idle if the initial set coupler is jumpered?

Have you visually watched the fast idle cam/ thermowax system as the car warms up to make sure that it extends and pushes the cam off of the bellcrank? Something like that, anyway, it's all in the Haynes & FSM....

HAILERS

&*&*&*&*&*Hmm, relief solenoid valve being energized would just exhaust the air pump *&*&*&*&*&*&

Wayne, Wayne, Wayne (get ready), you've gotten that wrong once again. The Relief Solenoid is energized at idle with a warmed up engine. That Allows a vacuum to the relief diaphram to keep the air from being dumped overboard into the silencer. There's a free download of the fsm, online AND for FREE!

WAYNE88N/A

I knew that...Why did I type that?

I don't remember- it was more than 12 hours ago

Are you perusing every one of my posts these days?

Claynoyes

Today I put a mirror next to the firewall and watched the thermowax. I couldn't see where the plate alligns with the roller, but I did watch it as it warmed up. After about a MINUTE OR MORE of the 3k warmup, the thermowax started to push the screw, and the idle started dropping in small intervals. It drops from a smooth 3k to 2500 oscillating then to 2200 oscillating all the way down to about 1500 and oscillating. Once it was at 1500 and oscillating, I pushed the screw down with a screw driver to see if there was any more rolling for the plate to do before it was completely off the cam roller, but it did not change the idle at all, so I assumed that it was correctly adjusted.

And.. When the initial set coupler is jumpered, there is no change in idle.

Claynoyes

Today, I finally got around to doing the bench test on the AFM. It checks out ok.

I was wondering.... after driving my friends rex, i concluded that mine has absolutely no torque. I know they don't have much to begin with, but i can't even get my tires spinning when i rev to 4k and drop the clutch; it just bogs down. He did not have his power steering or air conditioning belts attatched at the time. Are the two missing accessories actually causing a rise in torque, or do I have yet another problem to work out? Just curious.

Thank you,
Clayton