26hp Efi hunts at idle..

From what I can derive from your information is you most likely have a Kohler CV26-79510 with o2 sensor of part number 24 418 05-s

Since no fault codes do some basic stuff the EFI engine takes for granted....no debris in line/tank. Perhaps substitute the pressure regulator with a another if you can avoid buying one. Injector(s?) could be dirty or have a weak spring. How about a cold start injector that won't turn off ( dirty or worn out?-if fitted) and keeps supplying over- rich mixture? If there is one it is controlled by a temp sensor probably screwed in somewhere on the engine. The sensor is a variable resistor which provide current to the ECM which triggers the cold start injector. The test is to put the sensor in water and slowly heat it while hooked to your DVM. It should put out a varying voltage. Don't let this scare you off. If this applies it is an easy test is you have a DVM (digital volt meter).

I emptied both tanks and installed new fuel filters and fresh fuel before I started anything.

I thought Id try unpluging the o2 sensor and install some fresh plugs. I ranit for about 15min. before it just died....low battery voltage

So I guess for now I'm going to charge it, check the charging voltage...i just want to mow my lawn

Out of curiosity I went to OPEengines online where there are free PDF downloads manuals for various Kohler engines. I looked at an ECH 650 service manual and it is pretty good. The EFI system does have SW diagnostics available, but probably expensive. I did notice "blink code" mentioned in the efi trouble shoot discussion. That is a diy aide. In the older car systems you simply ground two accessible pins which accesses fault codes stored and they "blink" their numbers with a little led. I have used this for years on a 1991 car I have.

Anyway I noticed they do discuss fuel injector problems in the text and also that that engine has an oil temp sensor which may help the ecm know how rich to make the start up mixture. There is a section for component testing with a DVM of various sensors which can save a diyer $$. I suggest you find your specific manual and take a look.

Thanks motoman. I'm doing some reading now

So, I wasn't cycling the key while looking for codes. Threw a code 22, TPS value improbable. I cross referenced the number and found that a 1997 volvo 850. I should have it monday.

In the meantime I'll try to calibrate it

I'm not of any help on the plug except to say that on cars the OBD1 and OBD 2 have the connector plugs just under the dash for easy access. And a distant memory of an old Pontiac . It did matter on it that the correct two pins were jumpered to read the blink codes. I wonder if you dare to simply start the unit and see if the system accepts and learns?

Edit: Some surfing...several good manuals on CV 740, ECV 630 available. IL ENG is right. There are various (Bosch) ECUs different pin outs etc on different units. There is info on TPS initialization down to the pin. I did not see any "manual" calibration instructions, but if you could find out the min voltage with idle arm set and then WOT it might be possible to set it manually. There was some chatter about loose throttle shaft problems . I looked at manualslib.com and manualmachine.com. Just for ref a car site had initial V at .46 and max 4.6 V , but only a refresher (for me) as to what the TPS puts out. Also earlier Kohler used a "brush" contact, but later TPS use a magnet.

When I said calibration, I meant the setting of idle and then touching (off memory here) pin 24 and 13(battery voltage).
It's a 24pin Bosch ecu. I suppose I could try jumping it at the ecu. But that makes me a but nervous for some reaso

Tonight I'll check and see what I get for voltage at min and wot

Sssooooo, I relized last night that I had forced the throttle open, not closed to idle. Forced it to idle and did the reset procedure...I didnt see the light blink but I went ahead and fired it up anyway. Started right away and idled at 1400-1300RPM before settling into about 1150rpm after about 2 minutes. I left it running for about 20 minutes and ut never fluctuated more then 50 rpm.

Thanks all for the help!!

Now on to fixing the leaks...