Idle issue.

Hi Dr djet, it's Nigel back again.I have had my ECU rebuilt by Bosch Classic,and a engine rebuild. The car starts and runs well apart from when coming off the throttle the revs dive down to almost zero and back up again, The TPS  was wrongly set when I collected and I could not set it to less than 5.6.After resetting the TPS to 2 percent I drove 30 miles and retested it had gone down to 1 percent .Pre last run I set it at 2.8  ,it seems u nless the idle is at just over 1000 rpm the idle wants to keep going too low.After another motorway trip I came home left the car for 10 minutes  did the usual hot start routine  ,and whilst opening my garage to put the car away,I could hear the engine surging   ie reving up and down quite slowly .What do you think is the cause ? Thanks Nigel

Hi Nigel,

sorry but I have forgotten about your case. But idle should not vary as you describe it. I would check your AAV and other possible vacuum leaks.

With correct TPS setting your engine should run well if you adjust idle mixture via rheostat. I do not understand what you set with TPS. It only signals idle and acceleration to ECU.

Hi Dr Volker ,thank you for your reply AAV Is that valve which closes as the engine warms up.? Would a smoke machine put into the throttle be a good leak detector ? Thanks Nigel.

Hi Nigel,

yes and yes . But open throttle then.

Hi Dr Volker,thanks for that.One other question,the engine was balanced but I was surprised to that that at idle it does have a slight rocking.which I can feel in the car.The rubber engine mounts must be 40 years old but look perfect .Is the above normal .or do you think it's another issue .?

Hi Nigel,

that is an issue. At our workshops you would be able to see how each cylinder performs and understand where the problem is.

Find a good workshop that can measure ignition and exhaust per cylinder.

Thank you for the information. Out of curiosity where is your workshop in Germany ?

Hi Nigel,
Volker doesn't own a workshop. He organizes days of information about the system where you get tips and maybe some help if you come with your car.
You find info and dates above, next to the logout-button.

I have two additional tips for you.
- let the engine run at idle. Remove the electrical connection from the injectors one by one. Maybe you find out the cylinder that doesn't run properly.
- Do you have the original distributor installed? What about the points? If they look like this one (#1!)
they have to be replaced because they won't give accurate contact any more.
I once had this issue at my car with R6-engine - the idle wasn't perfect anymore.

Regards
Norbert