broccolini

I think it's time to start dealing with my idling weirdness. Car is stock 1985 gsl-se. 184,000 miles.

I've been doing a lot of reading about idling problems, but I haven't come across anything like mine. It's possible I have two separate issues, I guess.

My car starts and warms up fine. It drops down to about 900rpm and idles steadily. After driving for about 5-10 minutes it will jump up to 3500rpm. It's not jumpy or anything. Just steady at 3500rpm for about a minute. I've tried tapping the gas pedal when this happens, but it doesn't help. Once it drops back down to normal idling speed, it's steady again. This has never happened more than once in one trip, and doesn't happen every time I drive it.

If I drive the car for a while and park it for a short time, it idles low and erratically for a bit and I have to use the gas to keep it from stalling when I start it again. Once it's done with this, it idles and runs just fine. This only happens when the engine is warm. It's never done it starting cold.

I've changed the plugs, wires, cap, and rotor. I have all the fusible links on order and will replace those just in case it's a weird electrical issue.

Should I be looking for a common cause to both of these symptoms or is it more likely to be two different things?

Thanks for any help.

LongDuck

Two different things; the first issue of the high idle, that's likely to be a sticking fast idle cam. When you drive the car, if the fast idle cam gets set when it shouldn't it will bump up the idle speed as if it were a cold start. The normal cold start procedure is to get in, press gas pedal all the way to the floor, RELEASE IT, and then crank until start. The reason for doing this is to set the fast idle cam, which will help with cat heatup time for emissions, and also help warm up the engine to get some heat in your coolant to warm the cabin. The fast idle cam is controlled by the Thermowax Pellet at the rear of the throttle body which receives vacuum signal from the intake manifold, along with sensing throttle body heat provided by coolant lines coming from the back of the waterpu p and going to the rear housing as a return. When the engine is hot, the wax pellet melts, releasing spring tension which holds the fast idle cam in contact with the throttle body rod. You can see this cam surface near the front of the throttle body facing the front of the car.

Your second issue sounds to me like a temp sensor - either intake air temp at the airflow meter or dynamic chamber, OR coolant temp sensors on the radiator or back of the water pump - which tell the ECU how to apply an injector fuel map to keep the engine running properly. It could also be the BACV located on the dynamic chamber which adjusts bypass air based on solenoids immediately below it. The BACV can get dirty with carbon and cause the diaphragm to stick, thus stopping its ability to bypass air.

start there and see what you find,

broccolini

Ok. Thanks. I'll start with the fast idle cam and see if I can eliminate that problem first. I'll need to verify this later today, but I don't think it idles at 3500 when I first start it. And I do push the gas pedal down once. It idles higher than when it's warm, but it might be about 1500rpm when I first start it cold. Should it be at 3500 when it's started cold with the fast idle cam engaged?

ETA: Well the car made a liar out of me this morning. It did the varying idle speed when I first started it cold. Jumped from 1200-1600 a few times. Then it did the jumping up to 3500 twice while I was driving. I don't think this changes my approach to dealing with it but I just wanted to be precise.

broccolini

The fast idle cam seemed fine. It moved freely by hand. I cleaned and lubricated it. Is there anything else I should do to it?

LongDuck

Search on my uswrname and "surging". It sounds like your throttle rods may be sticking which creates an air powered feedback loop that results in a rapid rise and fall of rpm. If they're sticking at a particlar place, it can cause the specific rpm you state, which would be random.

broccolini

Thanks. Is this something I'll be able to find in the FSM? I don't really know what/where the throttle rods are.

broccolini

Ok. Cleaning and lubricating the fast idle cam did not help. I'm going to clean the BACV next and try to figure out the throttle rods and get them lubricated.

I think I read that the vacuum selenoid can also cause problems like this? I'll check those and the temp sensors after I take care of anything that can be cleaned.

LongDuck

It's not in the FSM. Surging is caused by the steel throttle rods (the rods that hold the butterfly valves, and rotate in order to let more/less air into the intake) running inside unsleeved aluminum holes in the throttle body. This results in galling of the aluminum by the steel, formation of aluminum oxides - which are highly abrasive - and a resulting increase in friction of the throttle body rods which causes a delay in their vacuum activation by the Vent and Vacuum solenoid valves.

The solution is to remove your throttle body (4x10mm nuts, plus the 2x10mm chrome nuts holding the air pipe in place, and the throttle & cruise control cable), and then lubing the inside of the throttle body rods where they go through the throttle body. Lube with something oily, not a degreaser - which will only make it worse. Turn the throttle body 90deg each direction to allow the lube to flow into the joints, and then reassemble. Usually, this provides enough lubrication to allow the throttle rods to respond a little better during fine throttle manipulation and when the solenoids are trying to compensate idle for one reason or another.

As mentioned, searching on my username and 'Surging' would get you this same information, so I saved you a little time. Also read this FULLY: http://mrmazda.no-ip.com/gslseidle.html

...and try to avoid playing with the Idle Air Control Valve - which doesn't, along with the Idle Mixture Adjustment - which won't. Most people get an -SE and immediately start tinkering and totally screw up the idle control air circuit. Don't be THAT guy!

broccolini

@LongDuck, I did read your other posts about this, but I couldn't figure out exactly what the throttle rods were. I was looking through the FSM for a diagram of the throttle body to see if I could find out. Your explanation here makes it clear though. Thanks. I think I know what you are talking about now. I have some light machine oil that I can use.

I also read that link you added several times. I haven't adjusted anything because of it. The boy who owned the car before me thought it was a TPS issue. He bought a new one but hadn't put it in. I still have it, but after reading everything, it seemed like there were a lot of other things to eliminate first.

Thanks again. I'll update this with any interesting results.

GSLSEforme

" The boy that owned the car before me thought it was a TPS issue-... and it very well could be.
Strongly suggest you begin your diag/testing here,before you start taking anything apart. People(a lot) underestimate the driveability problems that arise from a misadjusted/glitchy TPS . Some of your driveability complaints are exactly the type emanating from tps problems.

Familiarize yourself with operation/testing of TPs in FSM. You'll want to ohm sweep and test reference voltage input and output. Backprobe the TPS connector with a multimeter with key on and manipulate wire harness on both sides of connector and watch meter readings for dropouts or sudden changes in resistance,this could indicate a wire break/loose connection that could put you onto the reason(s) for quirky idle and more.

The TPS is very reliable,have not seen too many fail,but they do wear out and your car has near 200k on it. Since you already have a replacement(is it a Mazda oe part?),switch it out,adjust it properly and see if it addresses your problems.
Mazda had a special tool for this,but you could use a pair of multimeters to do the same thing or my preference,the 2 light method by making your own version of Mazda's special tool. Couple of # 74 bulbs, some short lengths of wire and three male spade terminals.
I'm away from home currently,when i get back i'll take a pic of one i made to show you what it looks like.

broccolini

@GSLEforme. I've read about making a TPS tester/adjuster but all the threads were so old there were no pictures. So pictures would be great. I'll test the old one once the procedure makes sense. I think the new TPS is a Mazda oe part. I'll take another look at it.

I wasn't ruling the TPS out, I just didn't want to overlook other things. But testing it seems like a good idea. I'm trying to go through things in the right order, one at a time so I know for sure what fixed it.

KansasCityREPU

iTrader: (9)

Here are a couple of pictures of my tester. It's just a couple of lights with the hot leads put together. Dosn't mater which leads though.

broccolini

Thanks for the pictures. It makes a lot more sense when you can see it.

GSLSEforme

A crude version of tps adjusting tool i made while at a friend's helping with his RX. Uses #74 dash light bulbs availableat most auto parts stores. Solder wires to each wire on base of bulb,heat shrink in place and male spade terminals on other end. Basically a throw away,i've misplaced many over the years.

broccolini

Ok.
I tested the TPS on the car and my readings were 2.3k-9k. This was not correct, so I replaced the TPS. I made a tester and adjusted the new TPS.
The car is running much more smoothly now. It was idling a little high after replacing the TPS so I adjusted that too.
I haven't taken it for a test drive aside from running around the block, but it's a lot better at low rpms and I didn't have any idle bouncing.
I want to take it out longer before declaring this solved, but I am optimistic.

Also, testing and replacing the TPS was really easy. I feel a little dumb for not doing it first, but I kept reading about how they were pretty reliable and I shouldn't assume that it was the issue. I guess it didn't hurt anything to do all the other stuff and I learned a lot.

Thanks for the help.

GSLSEforme

Good on ya!

LongDuck

Nice diagnostics! Recognize that the TPS has a carbon strip on the inside that determines the resistance in the circuit. Under steady state driving conditions, that center section of the strip gets worn over time and will eventually lose continuity or throw erratic readings back to the ECU. When that happens, occasionally, adjusting it will help, but the only fix is a new TPS. I noticed this on my original TPS when it would idle just fine, but under cruise control on a flat, straight road (common in the AZ desert...), the engine rpm would hunt up and down just slightly but enough that you could feel it. Very annoying, and somewhat difficult to diagnose.

I keep my TPS light rig in the glove compartment, and have found the best adjustment position to be when the 2nd light just barely goes out under throttle body spring tension. Adjusting to the FSM spec always seems to leave my car hunting at idle, or with poor just-off-idle acceleration.

OP: Post back in a week and confirm that this fixed it, and thanks for sharing your story.

broccolini

[QUOTE=LongDuck;12262320
I keep my TPS light rig in the glove compartment, and have found the best adjustment position to be when the 2nd light just barely goes out under throttle body spring tension. Adjusting to the FSM spec always seems to leave my car hunting at idle, or with poor just-off-idle acceleration.[/QUOTE]

That's interesting. The FSM was a bit vague on this. If there are no lights on and you adjust it up, you aren't in the same place as if there are two lights on and you adjust it down. I put it in both conditions and set the screw between those two points. I'm going to leave it there for now and drive it for a while. But that's good to know if I'm still having problems. Thanks. I will keep this post updated if anything comes up.

MikeCT01

I know this is an old post... but I have a question (or two).
The guy I bought my 84 GSLSE from had his 'mechanic' work on it who 'didn't really know the RX7 all that well' and they did some creative vacuum hose routing. Strangely enough, the car idled somewhat smooth, so I did not discover this right away until my AC was back up and running and it was doing a whole bunch of interesting things.

Using the vacuum line diagram, I corrected the line routing. Next, when I started the car cold, rpm go straight to 3k and stays there till warm, which it did not do prior to vacuum line fix. When it did warm up, I had the bouncing idle.

So, I will read through the TPS stuff mentioned previously, but I want to know is that 3k at cold start normal? Seemed kinda high to me, but this being an RX7 and all...

LongDuck

What you describe is not this issue, but create a new post and we can discuss it there.

Necroposting doesn't help the forum, and only complicates future troubleshooting when users are asked to 'search'.