grotto107

1985 GSL-SE 150,000 miles. Starts and idles smoothly at 800 rpm. Once car reaches 2000 rpm the problem starts. At cruise sounds like it's running on 1 rotor. Pull over and the car is idling steadily at about 2100rpms with the clutch in. In neutral with the clutch out it surges between 1500-1700 rpms back and forth. Depress the clutch and it climbs back to a steady 2100 rpms.

I can fix it by blipping the throttle. It goes back to 800 rpm idle until I drive it over 2000 rpms or so, and the problem's back.

I can also fix it by a hard knocking on the top of the throttle body. I suspected hanging throttle valves, but both the primary "stop" on the side of the throttle body is all the way back as is the "stop" on the little rod that controls the secondaries, and it's still surging. I did notice in the FSM that it said the secondaries are supposed to open when the primary is open 15 degrees. Mine are open all the way when I cut the car off and remove the tunnel to inspect them.
I thought of watching them with the tunnel off, but the car won't start with it disconnected.

I think I've read all the posts that will still open in the FAQ page. The "ILUVMY RX-7" article and the Mitchell Manual are gone. I've read the other 5 posts that I was able to find.

I've cleaned the rods in the throttle body with carb cleaner and then lubed them with thin oil. I've removed the BAC valve and cleaned it . I also tried plugging the large hose to it which fixed the problem for Gump in 2002. I've put my finger over the intake to the Vent Solenoid valve. No help. I disconnected the harness to the 2 solenoids with the headlights on per the FSM, but the rpms don't decrease like the FSM says they are supposed to. The fast idle cam is not touching the roller at idle. The throttle sensor checks out at about 1000 ohms at rest and 5000 wide open.

I think I've located the thermowax pellet, but I can't tell if it's sticking . FSM didn't say how to check it.

Maybe I've missed something. Need some help from you guys smarter and more experienced than I. Thanks.

Whisper

I've had this exact same problem.

First of all check the little cam on the throttle rod, one that pushes the TPS in, and make sure it has zero play. What happens sometimes is the metal hole on the cam, with which it slides onto the rod, wears out and widens over time, causing the cam to be loose, and as a result it kind of sticks a bit and doesn't press the TPS down enough to trigger the idle control. It confuses the ECU, which starts to cycle the revs, because it's conflicted about whether or not it's supposed to idle. If you blip the throttle, the cam probably returns to proper position.

Another thing to check is vacuum hoses going to the solenoids which control the BAC - make sure they're not clogged. Also pull the solenoids and test them several times, to verify they work consistently.

And obviously check for any vacuum leaks.

If you want, you can disconnect the BAC vacuum hose (the big one) and plug the holes. If you do that, the car should have a stable idle, since ECU can no longer compensate, but that's not really a solution, because it'll bog down when you use any electricals.

Oh, and pushing the clutch in simply releases the transmission friction, allowing the engine to spin freely, so it revs up to over 2000 RPM. I think at that RPM range the BAC control is ignored, which is probably why it idles smooth there.

One last thing, check if your distributor is installed correctly.

grotto107

Thanks. I'll check all this weekend. I know it's not the distributer, because it hasn't been removed. I 've already plugged the big hose going from the plenum to the BAC valve and the inlet to the BAC valve which didn't help. I hope it's that cam, because that'll be the easiest fix.

Ark1

85 GSL SE.

Engine surges, goes through lots of fuel. Doesn't really perform well. Turn and adjusted every screw, removed plenum checked injectors, changed limit switch, the list goes on.

There is condition in which the ECU can do what you are describing due to a back feed in the electrical circuit to the ECU. Stay with me here because the fix is so simple and the headace that I had with weeks of diddling around mounted to this.

Get an electrical diagram of the engine control circuit that shows the supply to the ECU.

Find the fuseable link near the battery and remove it. Now jumper out where you took out the fuseable link, it is little section of cloth covered wire held in with two push on connectors. Don't take voltage readings because the back feed will fool you into thinking there is power. ( I am an electician I know it fooled me) Jumper it out with a short section of wire and see if the surging goes away and the idle comes into spec. Of course you may have turned every screw like I did and have to adjust a few things. But the fuseable link on this old car just rotted away, at first the problem was intermitten but finally came and stayed.

I swapped out the ECU, the Dizzy, the throttle posistion limit switch, the BAC valve, Mass air sensor, injectors, barametric pressure sensor and every solenoid in the spyder. I also installed a spring to try and close the throttle butterflies, Oh and I changed the throttle body from a donner car as well.

Go right over to that link remove it and jumper it out. Chances are that you will have to buy a new one but your problem will be solved.

TonyK.

Grimsby Ontario Canada.

grotto107

Checked the throttle shaft cams and there's no play there.
I haven't checked the 2 solenoids repeatedly yet.
Here's a puzzler- The car has acted up consistently for about 2 or 3 weeks now. every single time I drove it which is at least once a day. Yesterday the temperatures broke here in N C. Had been 20-40 degrees . yesterday I drove the car when the outside temperature was 52 degrees. Ran perfectly. No problems. I wonder if this could be temperature related? Or maybe just a fluke. I'll drive it again today and try the fusable link by-pass if it will act up for me.

arghx

iTrader: (3)

Have someone watch the TPS voltage as you drive the car. You may want to use an analog meter because you won't have sample rate issues. That will tell you if the throttle plates are hanging up.

arghx

iTrader: (3)

Also, about the fast idle system: the fast idle system was a similar design from series 3 GSL-SE all the way to the 99 spec series 8 FD. Mazda didn't really change the throttlebody's basic design much.

this is from the 84 training manual:



Let's say the thermal wax is malfunctioning for some reason. If you rotate the cam up, TPS voltage will drop and the throttle plates will close. If that eliminates the problem then you need to adjust the "cam adjusting screw" so that the fast idle system will behave similar to the graph.

grotto107

Problem is not temperature related. Drove it today at 29 degrees outside and it's still working perfectly. The only thing that I did to the engine yesterday was to fiddle with the various cams, tps, and linkages toward the front of the car to see if the cams had broken away from the throttle shafts. Don't know what I did, but it's running great now.

arghx, how do I tap into the tps to read the voltage while driving the car?
I checked the ohms at rest and wide open , but I had to disconnect the tps harness to insert the VOM probes.

Whisper

Chances are the problem will come back, since you didn't actually fix anything.

Typically it's not a consistent problem and it happens intermittently.

arghx

iTrader: (3)

Backprobe the tps pin at the computer

Ark1

This is still sounding like a fuse link problem. Had the same issue, car runs like crap then one day it is okay and that was because the connection was being made by the strands at the ECU fuseable link. Intermitten problems are normally electrical.

TonyK.

grotto107

I'll inspect the fusable link and report. Thanks to all who are helping me here. John

Ark1

I fell into this trap and a guy on this form early before I started swapping every thing on the car suggested check the fuseable link. Like a dumb *** I though get real. I am an electrician and this guy is trying to tell me how to look at a fuse? I expectd to see the link fried. A good link or a bad link looks the same. I looked at the thing with my eyes and said doesn't look bad and went on to spend weeks swapping out parts and getting totally frustrated. In desperation I took the link off of the car and used a spare link from another donner parts car. Started the engine and it has been fine for 3 years. Good idle and lots of power.

Just do it, change that link or jumper it out with a length of wire for a short time. Take the dam thing off and the car will still run like crap but it will still run. The car isn't wired like you may think. As and electician my thoughts were that remove that link and the ECU won't work and the engine will not start. Wrong.


Sorry for being a pest. But if you knew how much time I spent trying to solve what you are decribing and I resisted checking that dam link that solved all the problems in 30 seconds, well I have said enough.

TonyK.

grotto107

I'll replace it whenever it stops raining here (no garage or carport). Thanks!

grotto107

Ark1, do you remember which link goes to the ecu? My car has 5 of them beside the battery.

grotto107

My wiring manual is very confusing. It shows 3 links on some pages and 1 on others. Nowhere does it show all 5 and what they control.

Ark1

According to the wiring diagram the Fuel Injection system is controlled by a white wire with a red tracer.

But looking at the Fuse Links the top one looks the newest. So it is either the top one or the 3rd from the top.

My problems started when I was refilling the A/C compressor and had to route the A/C manifold guage hose near the Fuse Links, Just bumping it cause it to go open and that is when all the problems started.

TonyK.

grotto107

Thanks. I'll start my search for the links later this week. My local Advance Auto doesn't sell them.