Is it normal for our engine to vary in idle slightly? From about 780 to 900rpm . Every 10-20 seconds it settles down (it doesn't drop) to around 780 rpm and sits a second or two then drifts back up to around 900rpm. Also a slightly sluggish blip of the gas at idle makes it hard when at at stop on a hill. Any thoughts.

Note:
this engine only has around 700km on it.
Bennet built coil upgrade
Gutted cat
Mazda speed cai

 

Is your HVAC set to defog or is the A/C on?

Either one of those will cycle the A/C compressor periodically which can play with the idle a bit.

 

Ac? I got rid of that. Don't really need it around these parts. And no nothing else is on and the batt is a red top and only a couple weeks old. I doesn't effect driving except for the slight delay in response from a stop. Again I'm talking miniscule delay. I find it's not there when the idle is at the higher point. Is there anything I can do to make it idle around 950rpm. Besides ap since I don't have one. Has anyone tried to sand the edges of the flap in the throttle body the allow for tiny more air at idle. I have two working TB so I can experiment lol.

 

How did you get rid of A/C? If the compressor is still connected and has a belt on it it might think it's still using it. Even if the rest of the system is gone.
Because this blipping sounds EXACTLY like normal AC cycling.

There shouldn't be any delay even at 750 rpm though.

 

I didn't put the compressor back on when I put the engine in. So no belt. Just the one for the water pump and alternator from the main pulley.

 

Are you looking at the RPM gauge or a phone app? The RPM gauge stays pretty steady, but a phone app will show something like the variance you describe.

 

Both obd and the rpm guage shows it. There is a small shake when its on the lower end of it. Around 800rpm. But a lil higher and there is no delay and is smooth as can be on take off.

 

I know someone who used MazdaEdit (I think) and adjusted his idle to 900-950 and its super smooth. It is also a Pettit Built engine so theres that

 

I do not have a cobb so I can't change the tune. I'm still debating on trying to file down the edges of the flap in the throttle body. I don't think it would take much to get idle a little higher. Or if it would make the idle higher at all. The ecu will probably just calculate that extra air and dial back trims.

 

If you want the bearings to not wear through you’d be smart to raise it to at least 1,000 rpm

 

Do you think sanding down the edges of the throttle plate would raise idle? Or is there a way I can without a cobb.

 

No, the OE system is going to try and maintain the set point in the program software. The issue at OE idle is oil pressure. The alternative to that would be to modify the oil pressure regulator. Mazmart sells that. It won’t change your idle situation though. You’ll need programming software for that if you also need OBD2 emissions compliance. Otherwise an aftermarket ECU like the Adaptronic Select could also be used.

 

I'll probably up the oil pressure and get a Cobb when I can