Runs rough for 20-30 minutes then smooths out

Reference my 87 328GTS (US Spec). I've searched the forums and on here and several CIS sites and have not been able to find this issue. Had a cold start issue that was fixed with a new protection relay and then a week later this new problem started. It just runs rough - sputters and stutters really badly, but slowly gets better after driving for a while and then after about 30 minutes seems to run fine. Since this is well past when the car is running in warm setting, it seemed strange to me. It also has a new behavior in that the idle used to be 1500 on cold start until warm but with this new condition it is idling at 1000 rpm even at cold start. I replaced all the spark plugs and fuel injectors and no change. I checked the voltage of the battery when off and during starting and was 12V off and 14V at start, which seems good. Still learning and hoping someone here has seen this before.
Thanks!

 

I ame no expert on F 's
Mine to always = cold or warm idle s at +/1000 rpm.
As for "sputters and stutters" i should say clogging injectors Butt as you have new ones in it it cant be the case.
Spark wiring?

 

Perhaps your AAV is sticking? Spray some WD40 into the AAV valve from both sides. The metal plate inside slides back and forth and can get hung up from corrosion or exhaust deposits (see next pararaph).

The air injection system has check valves on each bank's air injection pipes that can fail (the rubber flap inside perishes from the manifold heat over time), and you get exhaust gas backflowing into the system. This can also gum up the AAV.

There is a solenoid that controls the emission control related air injection system (it opens and closes a vacuum source that actuates yet another check valve, that in turn adds air into the exhaust stream - the large round plastic one near the oil filter area), and once the car has run for a while, the air injection is shuts off, so that may explain the symptom and point to some issue within the air injection system.

The air injection and AAV hoses are leaking and seal up once the engine bay gets hot? Are your hoses the rock hard cloth SAG logo braided originals? Try tighening up the hose clamps when the engine is warm after a drive and the hoses more pliable, the "spring" in the hoses sets after time and heat, and they may not be sealing well. Tightening when warm may help them seal when things cool down.

In any event, inspecting these components is not too much work, and worth doing to rule that system out.

The Throttle Position Sensor at the throttle body may need adjustment. When the car is off, you can actuate the throttle by hand and just off idle there should be a very faint "click". That is the TPS switch actuating. The TPS can be slightly rotated to position it to click just off idle. It may not be set up like that, and sends incorrect signals affecting cold start and run parameters. The TPS itself could be failed. There are some threads on how to test this using a multimeter, pretty simple to check.

Hope this gives you some ideas. So much of the cars systems are set up for cold running emissions compliance, there is quite a few signals being sent to the ECU to modulate fule/air for this purpose. Once the cars are fully warmed up (not just the short period beyond cold start) these systems have lesss impacts, and hence why your car runs better after being warmed to full operating temperatures.

 

Sounds like this problem.

https://www.ferrarichat.com/forum/threads/its-the-coils-stupid.698721/

 

I had a very similar problem in my 328, and it was an air leak. My gut says your air hoses are old, and cracked. When it warms up enough, they expand and seal up he cracks, and the air leak is not as bad. I would inspect the air hoses to and from the AAV, and then the cold start hoses... Before you spend any $$ on replacing or tinkering with injectors and or coils, etc.

You could have a cracked O ring on injectors, but then when cold you should smell gas very strong... my guy would be to check the air bypass system hoses. ....especially if you had a relay replaced, now that its drawing more consistent pressures, the hoses are under more stress when cold.... Hope this helps.

 

Thanks for the advice. I looked at the hoses and squeezed them and they seem reasonably pliable. However I will warm up the engine and tighten them to see if that helps. They look like they've been replaced at some point as none of them are cloth covered. The vacuum check valve controlled by the solenoid does look original - maybe I should replace that. Attached are pictures. Is there any way to check the functioning of these valves? I will also try the WD40 on the AAV.

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Thanks - I installed the injectors with new O-Rings. Will check the hoses as you suggest.

 

It does sound the same. I will research if there is a way to test the coils also.

 

Yes, those are not original hoses so they are less likely to be the problem unless the clamps just need tightening up. Check that 90 degree hose in pic three, no one replaces that as it is expensive and hard to find a non OEM that fits. The T that it connects to often rusts out from inside. And the exhaust air injection check valve in pic 3 does not look like an original, but looks quite old. In pic 4 that vacuum actuated valve is likely original (new ones are all black not the original ivory). You can check it by removing the vacuum hose on top, and putting on another hose and sucking/blowing on it, no air should come through it if the rubber diaphragm inside is still good. That also assumes the solenoid actuating the vacuum is working to open and close that valve as the fueling computer instructs it to.

 

The new coils are $$$, and are not quite the same as the originals (but work fine, but they won't accept the OEM coil wire retainer you just let the coil wire boot hold things up). The transistor module on the top is what typically fails, and was available to be purchased separately.

 

Add one can of BG44K fuel cleaners and drive

 

One easy thing to do is to connect the two wires going to the water thermoswitch on the coolant expansion tank together to simulate a properly closed cold thermoswitch to see if it makes any difference in the cold running after start-up. Its logic is:
cold = closed
warm = open
Your time element of 20~30 minutes seem longish for this to be the issue, but it's easy to do. Otherwise, the other thing at the top of my initial diagnostic list would be to measure the cold and warm control pressures of the WUR to see if it is working correctly or not. Good Hunting!

 

Checked the vacuum actuated valve - it works. Tightened air hose connections. Checked fuse box and there is a problem there, although I need to get it fixed, I don't think it's causing my problem.


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I'm thinking about the coil modules over the coils - speaking to a friend this morning at Cars and Coffee, he said he had a similar problem and the coil modules corrected it. Back to Frisky post above...

 

The problem with that is the fuse board overheats, delaminates and you can get connectivity problems at the fuel pump, which is what that burnt connector is typically connecting.

Try putting some Deoxit contact enhancer on those connector pins. It can improve the connection meaningfully, if it is not too far gone or the Board itself is too degraded.

GT Car Parts will be you new fusebox freinds for a rebuild with a modern circuit board.

 

Board has been shipped off to GT Car Parts. If the connection was unstable, this maybe could be the cause of my poor running condition? I guess I'll know in a few weeks.

 

I have the GT Board, it is a very well made item. My old board was working, but it was badly delaminated and I am surprised it functioned at all. In wet climates I suspect it would not have, I am a fair weather driver. Make sure you clean and Deoxit the old pins inside the connectors before installing. It appears you still have the original relays. When you put your new board in, or swap the positions of the same relays for circuits that are more infrequently actuated into those that are, the relays wear out with the number of on off cycles Get a couple of new spares and have a couple in your trunk in case one fails, there are two main types of relays on the board and both are readily available (albeit there are no metal casing ones left, they are all plastic). Do not discard the old metal relays, the concours guys will want good working ones long term when our cars become true art like collectibles .

 

Mine did not look so good either. Plus the burn through where the fuel pump connector is. I like the idea of holding onto all the metal relays - I believe mine are all original...
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New board back from GTCP last night and installed this morning. Car is definitely running better. Idle is smooth and correct now. I can rev the engine and it is smooth and correct, however when I drive and accelerate when cold, I get the sputtering and stuttering for about 10 mins or so. So even the time to get to a good running condition is now better too. Next step is I'm going to let it cool off and check the plugs and test them.

 

Replaced plugs - no change. Replaced ignition coil modules - no change. After 20-30 mins of driving cars run great, but up until then sputtering and stuttering. Just can't figure this out...

 

Just a shot in the dark here...

I watched a video SAMCRAC did on a Mercedes, ran like crap cold/at idle, ran great at speed.

Apparently there is a valve that redirects the exhaust back into the system, when it is at
idle the valve is supposed to be open, and under power closed, but the valve was stuck
in the wrong position at idle?
This might be too new of an issue, I doubt a 40 year old F-car has this kind of a setup,
but see if there is anything like this, some kind of EPA-forced emission setup?

 

Very surprised the coils didn’t fix it. The only other thing I did to resolve what seems
Like the same issue was have the WUR and Fuel distributor rebuilt at CIS. The coils
Made the biggest change, but the others helped.

 

I still say cracked air hoses OR - perhaps a o ring on the idle mix screw.... drawing un regulated air until everything warms up.

 

You could smoke test and look for vacuum leaks.

 

Reaching for less likely causes here. Maybe a fuel return line from the fuel distributor to the gas tanks is perishing inside, under its stainless braid. This could some injection system pressures to be out or order, and maybe when running a while the partially clogged line is eventually draining off.

You might also run some Marvel Mystery Oil throught the gas tank. This can remove some internal varnish deposits in the fuel injection system, there are really small tolerances in that unit. Won't hurt to try it. Same with some Redline fuel dewattering additive, maybe you have water in the gas.

There is an outlying chance that your fueling ECU is not working. But maybe just taking off the multipin connector, cleaning contacts with deoxit and reseating the connector would be worth a go to ensure the computer is able to send and rewcewive the necessary signals.

The crank position sensors are also known to degrade with age and heat, they are magnetic pickups.

Have you done a compression check, and valve leakdown check. When were your valve clearances last checked? Maybe when the engine heats up some marginal tolerences are causing the problem you are having.