High-RPM hesitation when Cold

[altmand]

Hello all,

Below is a challenging problem that numerous gurus have yet to solve:

1986 Spider Graduate (L-Jetronic) with 108,000 miles. The following describes the problem:

When cold, the car hesitates, as if governed, beginning around 3,700 rpm. As the car warms up over several miles, the "governer" raises its limit - eventually, the problem goes away. There is a sticking point at around 3,900-4,000 rpm, but once the engine is able to rev above 4,000 rpm, it takes only about ten more minutes of driving to have normal access to the entire rev range. However, the first number of trips above 4,000 reveals a sluggish feel as if the mixture is lean.

The following have been changed/checked:
1) new temp sensor
2) new fuel filter
3) new in-tank fuel pump
4) new plugs (what the heck!)
5) Auxilliary Air valve removed, cleaned, tested (works great) and replaced.
6) Fuel lines (metal and rubber).
7) VVT Solenoid - re-mounted - works great.

The car is driven daily. Regardless of the weather, it starts immediately, idles perfectly, and, if you are a short-shifter (below 4k rpm), you'd never know there was a problem with the car. The problem is very much temperature-related because the hesitation is worse the colder it is outside and therefore takes longer before it disappears. Once the problem does clear up, it won't reappear until the car has sat for over 12 hours. I have a used airflow meter on its way to me right now, but I'm not convinced that this will help.

Any ideas are welcome.

Thank you,

Drew.

[il_formaggio]

I think, some others may agree as well, to keep rpm's low for the first few miles of driving when you have a cold engine. How long do you let it warm up before driving off? I rev to 3K max with a cold engine until I see oil pressure start to drop. It takes along time to heat up 7.5 quarts of oil. You may be asking a bit much before it's ready to give.

[Hit an Apex]

Revving high with cold engine leads to death.

[altmand]

Thanks for the replies thus far.

While I concur thoroughly that 1) it takes time to heat up 7.5 qts. of oil; and 2) revving a cold engine leads to major problems, the issue I am having has nothing to do with asking too much of an engine upon startup. I do not floor it right at startup, nor do I abuse the engines in my cars; however, after a few miles of driving, seeking 4,500 out of an Alfa 2-Litre (in Florida) is not a great deal to ask. Moreover, while it is stupid to rev a cold engine to redline, the engine is at least capable of doing so when everything is otherwise working correctly.

This car has been cared for meticulously, and the problem came on rather suddenly without any change in driving style, location, fuel, or mechanical alteration/modification. The engine burns a bit of oil, but that is largely because the valves, stems, seals, etc. are original. The rings are in great shape and no oil (at least not any noticeable amount) is burned under acceleration. Oil is changed religiously at 3,000 miles or sooner.

Thanks again for the help.

[gprocket]

If your valve guides are worn I wonder if you are leaking enough oil through them to foul the plugs when it sits overnight. Try replacing the plugs with clean ones before taking the car out and seeing if the problem goes away.

- Rich D.