D21 idle surge follow up, please post your opinions

[72240z]

So This is a follow up to my last d21 surge problem post, please read that one if you have an questions not found here. Right or wrong w/e please chime in, after so many hours trouble shooting you kind of hit a wall and need different perspectives.

 

The other day after turning like 7 grand doing donuts and going crazy in the snow I noticed my valve covers were weeping, so today it hit 60degrees I decided to change them and while I was add it try yet again to diagnose this problem.

 

I cleaned all my grounds, check continuity in all grounds and connectors. I ran down the list of engine sensors checking each one by one as per all data instructions once again. Everything checks out, sigh AGAIN. This time though I had to remove the dizzy for the valve cover, so when all was said and done I broke out the timing gun and would you believe the timing is advancing and retarding itself in direct correlation with the surge and what I gather is also the direct reason. I was taken back when I saw that.

 

My question is what would advance and retard the timing the exact amount, aprox 15 degrees over and over AFTER the idle up solenoid kicks off, say 20sec? The only sensor I didn't get to check a 2nd time was the o2 and cas in the dizzy. Right now I'm thinking cas but this is my 2nd dizzy in like 6 months if its broke. The dizzy, cap, maf, chts have all been changed and a knock added. I disconnected the knock just to check, no change. So besides the cas I'm kind of at a loss as to what would be retarding and advancing the timing like that over and over and over under no load. Under load its fine. It's just REALLY annoying, killing my gas mileage and actually embarrassing I can't seem to fix it.

 

Also my friend disconnected the bat so I couldn't run the codes but last time I ran them I got a all is well and the surge was there. Cas would throw a code for sure, Idk maybe something is out of adjustment? I check and reset the idle. What about the maf, it BARELY checked out and was a bit sporadic to boot, I just don't think maf will cause this though. Anyway thats whats running through my head all tired and pissed lol.

 

Any help would really be appreciated, just throw logical shit out there I'll be more then happy to check it out and add it to the list. Thank you in advance.

[slodat]

Why not put this in the same thread, since it is related? Might get more or a better response.

[datzenmike]

The idle up solenoid is for when the air con is on and power steering, correct? Can you disconnect it to be sure that's not the cause?

 

What about the throttle position sensor on the Throttle body? It is slightly adjustable and may be slightly off.

[72240z]

Why not put this in the same thread, since it is related? Might get more or a better response.

 

Well I didn't want to bore anyone, the past post had a small turn out. I thought maybe a new one would attract a little more help. You may be right though, if this fails or slows up I'll bump the other. Thank you

[datzenmike]

Cracked hose/vacuum leak? Engine would appear to run lean on the O2 sensor at idle. Pinch all hoses close to t/b with pliers one at a time see if it goes away? Loose bolts?

[72240z]

The idle up solenoid is for when the air con is on and power steering, correct? Can you disconnect it to be sure that's not the cause?

 

What about the throttle position sensor on the Throttle body? It is slightly adjustable and may be slightly off.

 

Ya the idle up is for a/c, ps, and I believe when there is certain voltage levels being used like the fan on high, I have no a/c to check that aspect. All data says it kicks on for the 1st 20 seconds after start as well. I believe it to be a clue because it over rides w/e is causing this problem. The idle will remain constant for those 20 sec then the surging will begin. Originally this was the 1st thing I checked as it is integrated with the FICD or "Fast Idle Control Device". Both were a tiny bit off so both were replaced just to be safe. I did actually try reconnecting and disconnecting both just for shits and giggles with no change.

 

I ran diagnostic on both the tps and idle sensor, both are integrated. It's a 2 plug sensor, one modern rounded 3 pin connector for the tps and a bosch style for the idle. The one on it passed on the voltage range and continuity test but again for the hell of it I plugged in a z31 I had laying around and no change, same correct range.

 

These are what I thought to be the probable culprits when the problem 1st came to be but now that I have found the timing physically changing in front of my eyes I'm just shocked and lost. Imagine from tdc to 15 advanced back and forth as the idle goes up and down about 5-700 rpm, it's unnerving.

 

Thank you for the post.

[72240z]

Cracked hose/vacuum leak? Engine would appear to run lean on the O2 sensor at idle. Pinch all hoses close to t/b with pliers one at a time see if it goes away? Loose bolts?

 

When the problem 1st developed I did a check and found quite a few dry rotted vac lines that I either cut back or replaced. After that I got spooked and went to town with the cigarette method and the carb cleaner method. No trail with the cig and no idle change with the carb cleaner.

 

Again though with this new clue seeing the timing physically change I feel it would have to be electrical no? Idk anything mechanical that would change the timing like that in such an exact range over and over.

 

Thank you again

[datzenmike]

The timing advance may not be the cause, instead the cause may be causing the timing to advance. Just like any off idle increase on an engine with vacuum advance will send a vacuum signal to the distributor to advance the timing. Perhaps the ECU is just adjusting the advance in response to the idle increase.

 

So what will increase the idle? then?

[nukeday]

Here's a couple of long shots...

 

Long shot #1: I had a similar problem on another import, not sure how it might apply to your situation. You mentioned you've replaced the distributor so it got me thinking. From your description, it sounds as though there is a diagnostic connector in the the truck. Is it possible the initial timing was set without disabling the computer? What I discovered on my rig (Pontiac LeMans) was that the dizzy itself was actually installed about 3 teeth off. Jumpered the diagnostic plug to check the timing, pulled it out, rotated it a couple of teeth and that solved the problem. Very similar symptoms to what you describe, it took me a long time to finally figure it out. The computer was constantly trying to retard the timing at idle, I'm amazed the thing even ran, the window for that sort of driveability turned out to be quite narrow. For grins I pulled it in and out three or four times and set it in one, two and three teeth off to see what happened. Ran like crap until I got it right.

 

Long shot #2: Assuming this is an OBD compliant rig, what happens at idle if you disconnect the plug for the O2 sensor? I learned recently that the cycle time on these can vary, and is usually the minimum spec from stock, if it's been replaced. I want to say it supposed to be about 80 cycles p/sec. but the last one I threw on an O-scope was only about 50. It was brand new. The only way to compensate, that I'm aware of, is to install a PWM device to adjust the cycle time. Used O2 sensors don't really make any sense, but I suppose that might be an option, as long as they are a factory piece.

 

You seem to know what you're doing, so if this is obvious stuff, sorry. Sometimes a nudge in the general direction will set the wheels turning though. Good luck sorting it out.

[72240z]

The timing advance may not be the cause, instead the cause may be causing the timing to advance. Just like any off idle increase on an engine with vacuum advance will send a vacuum signal to the distributor to advance the timing. Perhaps the ECU is just adjusting the advance in response to the idle increase.

 

So what will increase the idle? then?

 

Ya thats a valid point. It's just after checking all these sensors Idk what could possibly do that.

 

Thats what I'm trying to figure out. I have been sick these past couple days but I bundled up, bit the bullet and ran the codes. It's throwing a cas code that it wasn't throwing it last time I checked trying to diagnose this prob. Maybe it hadn't learned it yet Idk but I picked up a dizzy from a 88 z31 turbo on ebay for 11 bucks. We will see if that does it.

 

I'm also not getting correct voltage from the o2 but I think it was because it wasn't warmed up enough. Was like 20 degrees, way to sick to be out there to check but when the dizzy gets here I'll install it check the o2 again, clear the codes and see what happens. I'm fairly certain the o2 would throw a code if anything.

 

Another thing I noticed while reading through the wiring schematic is the o2 ecu signal goes to the egr control solenoid then to the ecu. That could be causing issues too. The egr is eliminated so I'm just going to bypass the control solenoid and let the o2 go direct to the ecu. Or maybe jumper the control, something Idk, I don't like my o2 signal going through an inactive sensor on its way to the ecu lol.

 

Anyway I hope its just a 2nd broke dizzy and that this one coming will FINALLY fix it. I will certainly let you guys know. Thnx again

[72240z]

Here's a couple of long shots...

 

Long shot #1: I had a similar problem on another import, not sure how it might apply to your situation. You mentioned you've replaced the distributor so it got me thinking. From your description, it sounds as though there is a diagnostic connector in the the truck. Is it possible the initial timing was set without disabling the computer? What I discovered on my rig (Pontiac LeMans) was that the dizzy itself was actually installed about 3 teeth off. Jumpered the diagnostic plug to check the timing, pulled it out, rotated it a couple of teeth and that solved the problem. Very similar symptoms to what you describe, it took me a long time to finally figure it out. The computer was constantly trying to retard the timing at idle, I'm amazed the thing even ran, the window for that sort of driveability turned out to be quite narrow. For grins I pulled it in and out three or four times and set it in one, two and three teeth off to see what happened. Ran like crap until I got it right.

 

Long shot #2: Assuming this is an OBD compliant rig, what happens at idle if you disconnect the plug for the O2 sensor? I learned recently that the cycle time on these can vary, and is usually the minimum spec from stock, if it's been replaced. I want to say it supposed to be about 80 cycles p/sec. but the last one I threw on an O-scope was only about 50. It was brand new. The only way to compensate, that I'm aware of, is to install a PWM device to adjust the cycle time. Used O2 sensors don't really make any sense, but I suppose that might be an option, as long as they are a factory piece.

 

You seem to know what you're doing, so if this is obvious stuff, sorry. Sometimes a nudge in the general direction will set the wheels turning though. Good luck sorting it out.

 

Hi, thank you for your ideas. Sadly though this is pre obd1, completely dif animal. No diagnostic port, running codes off the ecu itself with led lights. False codes, no codes, old codes and only like 15 codes it recognizes anyway so its really a PITA. 80's tech at its best.

 

If it was obd1 I would be very happy, I would plug my reader in and the problem/s would present themselves lol.

 

On a side note the z31 has a diagnostic port but still pre obd1, you have to have this weird reader form Nissan. Nissan is the king of stikin it to you lol, esp in the 80s. I bet is was more an experiment then anything because you can read the codes off the ecu anyway.

 

Thnx again

[72240z]

So update, I (after about 6 months of searching) came upon a 89 vg30i dizzy and snagged it for 30 bucks. Happy to say the surge is gone. I actually had to retard the timing because the idle is so out of wack from all the tinkering I did to keep the truck driving with that surge but so far so good.

 

After that I thought to myself well is all data AND the factory manual wrong and the vg30e/vg30i dizzies different? No, BOTH of the ones I bought used have broken cas's, amazing. Another hard lesson learned......

 

Thanks again to everyone who tried to help, I appreciate it very much and a big FU to the ones who took the time to read and ignore.

[HRH]

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