355 low rpm problems

My 1997 355GTB its having low rpm (1,000 to 2,000) problems. At that range, the engine vibrates abnormally and hesitates. There is a strong odor coming out of the exhaust but no smoke. Above 2,000 it behaves normally.
The spark plugs (Brisk) were changed two weeks ago and the recall kit 48 (fuel block) was also installed at this time. Also the fuel filter and the air filters were replaced.
Today, I replaced the air injection pump fuse (it was blown) and also replaced the air pump relay. Furthermore, I "rebooted" the car (turn it off for a couple of hours and then turned it on). The car started up fine but after a little while, the vibration came back.
Any suggestions? I would prefer not to tow the car to the shop but I'm afraid to drive it like this.
Would appreciate any comments.

 

How did it run before you changed the plugs?

Any possibility you cracked a spark plug insulator during installation?

 

It ran perfectly before the spark plugs were changed.
I guess its possible a spark plug insulator was damaged during installation, but if so, shouldn't the problem show up immediately?
If a spark plug connector is loose, would the symptoms be similar?
If for whatever reason one of the spark plugs is not working, can it be driven to the shop?
Thank you for your assistance.

 

Very good chance the insulator cracked during install and is discharging to ground now ...

 

I've seen where you only get a random misfire if you put a hairline crack in a plug (you will have a consistent misfire if it is severly cracked). It helps to use a socket with a rubber insert.

I suppose a loose plug wire connector could cause similar problems but is less likely in my opinion.

It could be driven to the shop if it isn't at a fast pace or long distance (as you could potentially damage the catalytic converter(s) ). I would base that decision on the severity of the misfire but it doesn't sound extremely bad from what you described.

 

Replaced the plugs today. Two of the Brisk spark plugs replaced were apparently defective. Replaced the Brisk with NGK and so far so good.
Thank you for your help.

 

You're welcome, glad to hear it was a simple fix

 

Plug wires are also a weak link on the 355 and can cause an ignition miss.