Remember2

Hi guys, I really need your help on this one. First of all, it's a periodic problem, so I can not easily check something - however the problem is still somewhat consistent. It's a '87 NA btw.

Problem is that once warm it starts to hesitate and stutter badly. It doesn't happen on the freeway at cruising speed, but as soon as I leave the freeway, it's there. The weird thing is, that this only happens after the car has been standing still for several days (it does NOT happen on a daily basis). Once the car has cooled down again (½-1 hour), I can drive it problem free for the rest of the day, and the next, and so on. No problems at all, until after the next stand still.

When the problem occurs it will hold an idle, and I can drive it home if I apply the throttle sloooowly. Driving it very very gentle it will start and go all the way to full RPM, however if I at any time give too much throttle, it will hesitate and stutter, and if I'm not quick enough to back off, it will stall.

I have already changed the reference and crank sensors and the throttle positioning sensor (all new and OEM). I have also tried a second working AFM. Spark plugs look fine, as does the air filter. And I have gone through most of the plugs in the engine compartment with contact spray, and tried a cleaner additive in the fuel tank.

No luck, and it's driving me crazy

Any suggestions would be very helpful, and greatly appreciated! Thanks in advance everyone...



EDIT (elaboration from post #5):

Thanks you guys! Could I ask you to argument as to how your suggested solutions are aligned with the facts that:

1. the car always drives perfect cold
2a. the car always drives perfect warm
2b. UNLESS it has been standing still for many days, in which case the problem appears ONCE
3. after cooling down (#2b), the car drives perfect both cold and warm every day (1 & 2a)

I feel that the solution is very closely connected to the scenarios above, and as I have already spend numerous hours researching many different solutions, I really need a suggested solution that support the scenarios.

All suggestions (supporting the above) is very welcome. Thanks in advance!


UPDATED => Post #15

Kerry Chadderton

Quick thoughts are fuel pump connections, FPR or its vacuum hose and DME temperature sensor. All three can be tested and eliminated rather easily.

odonnell

Try unplugging your O2 sensor, if you have one. That can also affect the AFR.

Dougs951S

if the problem is associated with the car being hot, its probably running lean. you need to find out whats leaning it out as temps rise.

Remember2

Thanks you guys! Could I ask you to argument as to how your suggested solutions are aligned with the facts that:

1. the car always drives perfect cold
2a. the car always drives perfect warm
2b. UNLESS it has been standing still for many days, in which case the problem appears ONCE
3. after cooling down (#2b), the car drives perfect both cold and warm every day (1 & 2a)

I feel that the solution is very closely connected to the scenarios above, and as I have already spend numerous hours researching many different solutions, I really need a suggested solution that support the scenarios.

All suggestions (supporting the above) is very welcome. Thanks in advance!

Noahs944

Have you ever cleaned out the air intake system & fuel system with Seafoam?

Remember2

I have cleaned the air system when I took it apart to change the TPS and the AFM. The fuel system has been cleaned with an additive as mentioned. I don't think an unclean system would create the symptoms described, but inputs are welcome

Jfrahm

Could be water in the gas, it can come out of solution every now and then and mess you up. If a dry gas additive makes it go away like magic that might be it. It might still come back until you work though it all.

Remember2

I now have a new FPR and a temp sensor on the way. I'll keep this post updated with the results. In the mean time, I'm still very interested in any inputs

gtroth

If you can measure the fuel pressure and its leakdown, and the resistance of the temp sensor before you swap in the parts that would be good.

Your symptoms are odd- I'm liking the water in the gas idea Jfrahm put out there.
And I'd start measuring everything I could thing of.

Good luck!

Remember2

Hi again,

So I changed the FPR and the DME temp sensor - and no luck. The car has an unstable idle, and when I push the throttle hard it dies immediately (with a bang from the exhaust). If I push it gently I can keep it going all the way.

Todays experience (as with every time it has been left for some days):

1. Cold start - no problem
2. 10 Minute drive to the freeway - no problem
3. 10 minutes of driving on the freeway (car is now warm) - no problem
4. Another 5 minutes of driving on the freeway - no problem
5. Leaving the freeway - HESITATION AND STUTTER when giving throttle
6. Hesitation and stutter continues until the car is shut down (drove around with these problems for 45 minutes)
7. Immediate start after shutdown (in the period of trial and error above) - hesitation and stutter
8. Leaving the car for an hour to cool down
9. Starting again one hour later (still pretty warm) - NO PROBLEMS
10. Driving the same route (#2 - #5) - NO PROBLEMS

Based on experience, if I leave it overnight and replicate the above tomorrow - I will have NO PROBLEMS. However, if I leave it for a week - problems are back

I'm really (really!) frustrated, so suggestions are very welcome. The updated list of replaced parts:

DME relay, air flow meter, crank sensor, reference sensor, fuel pressure regulator, DME temp sensor, throttle position sensor.

What to do?

Spidey944

Have you confirmed that your new TPS is adjsuted properly? Since it only happens when warm-ish and when you're coming off of a cruise speed, it's possibly binding/not hitting the closed position? When it's acting up, use your hand to move the throttle plate linkage and listen for the closed "CLICK".

I've said this before in other threads, but find a shop with a smoke machine. It's primarily used to find EVAP system leaks, but can be used to find intake/vacuum leaks also! Might cost you $60-120 to have a shop smoke test it for you, but it's always good to know everything is sealed up properly.

Remember2

I have - both the old and the new OEM replacement

I agree - however I find it hard to believe it's due to a leak - as it drives perfect under all other circumstances (same goes for the TPS)

Remember2

So just to confirm - NO PROBLEMS this morning - exactly as expected.

How can this be? What am I missing? Please help...

Remember2

Okay, so in fact I was wrong. I just tried the same test drive this morning - and it died after driving 25 minutes.

So it isn't necessarily related to a longer stand still. The car drove yesterday, but cooled down over night. Problems again this morning.

I have a new (used) DME unit on the way. Other suggestions??