1998 Mazda 626 Engine dies when pressing clutch

What is the role of Camshaft position sensor in the idle process? The self-made cardboard gasket between the sensor and the cylinder head cover seems to prevent the RPM to drop below 750 (dropped only a few times below that since the gasket was installed), though all the other problems are still there and the engine still searches the idle for a moment before finding it.

Every time the car has worked well for even a moment, it had involved the re-installation on the CMP (cam sensor). Feels like the engine just loses the correct information very quickly.

Crankshaft position sensor doesn't give any malfunction code, and as far as I know the car shouldn't even start if it has a malfunction?

Seems to be impossible to find the air gap specs for the cam sensor; I managed to get the importer's workshop manual sometime ago, but it doesn't tell it either. Maybe the valve head cover is just designed like it can be in only one position. When I take the sensor off and put it back, it can move vertically around 2 to 3 millimetres before the bolt is tightened.

I've sprayed the whole engine bay and every hose and gasket with brake cleaner several times to find the leak, but there doesn't seem to be any.

The dealership mechanics last time told me that the problem is likely the ECM, though they tested it and it was OK. And I can't believe that the ECM/PCM can go broken when installing the new engine - everything worked well before the installation; the old engine just leaked so much oil that it was cheaper to replace the whole engine than rebuild the old one.

I'm taking the car to the workshop for the last time next tuesday; The dealer's in the neighbor town has more experienced mechanics so let them give a try; if they can't find anything, no one can. Let's see what happens.

Thanks for the comments, I'll attach them to the list of things already done for the mechanic.

The problem changed it's nature.

Though the alternator was tested in the other three places, it turned out to be on it's end. With all electrics on the voltage dropped to under 8V in about a minute.

The 80A alternator was replaced with new 90A one, which was tested with the full load after installation.

The RPM now behaves like it should in normal driving.
The virbation was gone for half a day, but now it's back, maybe it's even worse.

It also seems that the NEW alternator/engine can't take the load. When I have AC, rear window heater and lights on at the same time, the battery light in dashboard turns on and won't go away even if I turn the electircs off. I have to restart the car when it appars to get rid of it. The headlights appear brighter when I hit gas pedal and when back to idle, they darken.

What on earth can screw the car's electronics like that? The sensors were all OK, they were tested today as well. I think the car's system should be able to handle headlights, AC and rear window heater at the same time. When I turn any of those on, the RPM drops quite a lot for a while, it almost sounds like the car is going to die, but it doesn't

I self-tested the behavior of the car with different electric devices on. I noted that only high-power device that did NOT affect much to the idle rpm and alternator light was the stereo system which I have installed ages ago. It has separate wiring, so can it be somewhere in the car's original wiring? It's weird though that as far as I checked the wiring diagrams, the rear defogger, headlights and ac system do not have common groundin points (if I understood it correctly). Where should I look? I already checked the wire connections in the main fuse box and the area near it, as far as I could see the wires before they disappear in the plastic covering.

I can't believe that the stereo system could be the cause; the system was installed months before the engine change and it didn't cause any problems. When the engine was installed, the stereo system power cable wasn't connected to the battery - I connected the cable back about a month after the engine swap, the porblems started immediately after the engine change. My amp is only 300 watts, and I've used it in my second car for ages with similar installation with no problems before this car. The amp is OK, I tested it on my other car and it caused no problems. The amp is now disconnected, but it doesn't change anything. I've even tried to get the whole radio off the dash to rule out mistakes in stereo installation, and came to the conclusion the stereo is installed correctly.

About the crankshaft pulley, I actually don't know. I bet the mechanic doesn't remember it either.

I take it to the workshop on friday, we try another alternator just in case this one has failed. I make sure all the correct voltage measurements will be done.

The alternator that is there now, was measured with the car's diagnostic system. The voltage was over 15V (seems a bit high to me) without a load and about 14, 6V with the full load including all the electronics on the car that can be turned on.

Can the ECU be damaged? Does the ECU determine the electrical load or is there a separate detector?

The engine was 30000 miles driven when I bought it.

The new alternator is now installed. Worked like an angel for a few hours, then started to vibrate like an earthquake again when at idle. When either rear defog or ac is on, the headlights (and all the other lights like dash illuminations, indoor lights and such) brighten when hitting gas and dim on idle. The stereo unit illumination is the only light that doesn't react the RPM.

The AC on without other electronic makes the car vibrate.

The car is now pretty good to drive though; sometimes when coming to a stop and the clutch is pressed, the RPM goes near the 0 line for a while, but not often. If all electronics are on, it does it more often. Usually the combination rear defog + headlights lets the RPM go too low for a moment before the car "finds" the correct RPM.

I also noticed that if you get the RPM really high (over 6000) when not moving, and then let off the gas, the vibration sometimes doesn't come back when returning to idle.

I think it really is a problem with electronics, but the alternator doesn't seem to be the whole truth. I can't believe that the car was desinged the way that you can't have rear defog and headlights on at the same time when driving in the city.

Can the alternator supplement be failing, like is there a possibility that a faulty belt tensioner or pulley could cause this?

Yesterday I had the battery negative terminal off for a couple of minutes. I put it back and the RPM started to missbehave like before. I can't imagine any solution to that, or could it be the PCM?

I wrote a list of everything that has been done and decided to translate it to english too.

I looked my receipts and found out that the search of the problem has costed me 1800 euros which is way over $2000. At the moment it has costed as much as the engine and it's installation have cost.

The xx.X numbers are dates (day/month), I use European standard for them.

Symptoms:
1) Clutch pressed; RPM ->almost to 0->over 1000->750 only when stopped
2) Vibration at idle. Sometimes doesn’t vibrate when started cold, but after driving a mile it sure does. The nature of the vibration depends on the electrical load.
3) Some belt makes whining noise; gets worse with RPM to a certain point when it stops.
4) The clutch pedal feels like it attacks the foot when letting go.
5) (Long distance)headlights dim at idle, especially with the rear defroster on.
6) The gas pedal doesn’t seem to react correctly when RPM is under 2000
7) The ignition sometimes doesn’t stop right after pulling the key out.
8) Malfunction codes: 0340 (not anymore), 1632, 1631.

Shop 1= The shop that changed the engine
Shop 2= Mazda dealer #1
Shop 3= Car electrical repair shop
Shop 4= Mazda dealer #2

20.8
Engine changed: Only the basic engine is new, the valve head cover and camshaft position sensor, as well as the supplements and manifolds are from the old engine.

22.8
Stalls for the first time (clutch pedal pressed when slowing down)

25.8
Shop 1
Changed Idle control motor, battery and motor grounding checked, throttle body cleaned

Shop 2
New ignition lock bottom ordered, so the car will start for sure when it stalls.

Noticed the vibration inside the car when at idle.
Air filter changed.

8.9
Shop 1
Changed ignition lock bottom and spark plugs.

3.10
Shop 2
Nothing found, negative battery terminal changed. Diagnostic codes 0340 (Camshaft sensor) and 1632 (Battery voltage low) Intake manifold gasket and vacuum hoses checked.

Stereo installation removed to determine if that was the cause. It wasn’t

5.10
The last time it has stalled when driving.

6.10
Shop 2
New Camshaft position sensor. Still gives the malfunction code.

8.10
New battery purchased

9.10
Stereo installations back – doesn’t change anything.

24.10
Shop 1
Timing belt checked, valve head cover gasket replaced

25.10
Shop 1
Changed camshaft pulleys from the old engine. RPM still misbehaved, but didn’t go under 750 for a few days. Symptom #4 went off for a few days too.

1.11
RPM started to go below 750.

24.11
Shop 2
Camshaft sensor connector. The malfunction code 0340 hasn’t appeared after that. Code1632 (Voltage) Still appears. Worked fine for a short test drive like after the pulley change. Next ignition and the problems came back.

9.12
Shop 1
Wiring from PCM to the CMP sensor checked, OK.

12.12
Shop 2
PCM Checked->OK, PCM to Alternator connection checked. Code 1632 still (Voltage)
The company who sold me the motor and the service manager talked about the thing over the phone and came to the conclusion that the engine should work OK, though the engine is imported from Japan.

23.12
Shop 3
Idle RPM raised to 1000. Didn’t help, the vibration got worse. I hoped they’d check the electronics but they claimed the problem wasn’t electrical

9.1
Korjaamo 3
IAC valve cleaned, idle RPM changed back to 750

Shop 4
EGR valve, fuel injectors and fuel pressure regulator changed.

9.1-13.1

Tried valve cleaner and injector cleaner with gasoline. No change. Noticed that the CMP sensor touched the camshaft pulley. Raised a bit with a cardboard gasket.

16.1
Shop 1
New ground terminal, wire and grounding point to the battery.

20.1

Shop 4
The alternator failed. 90A Alternator changed. Every symptom was gone. Idle speed adjusted with tester. No malfunction code after change. Before change code 1631 (PCM failed from over 20V voltage). 90A alternator was the only one that didn’t cause the whining noise.

Later that day the symptoms came back. RPM still behaved right, but the others appeared again. The alternator light came on.

22.1

Bought NEW alternator

23.1
Shop 4
New alt. Installed. Everything worked fine for a few hours

I drove about 60 miles on freeway and when I came back to the city, the symptoms came back.

PCV-valve checked, it was OK