Wideband readings at idle

[paddlenbike]

My A/F ratio at idle bounces between about 14.6 and 15.3. When it does reach the lower-15s the engine gets a little rougher and starts making the typical lean idle pop sound. I can add fuel with the S-AFC or turn up the fuel pressure, but eventually the ECU just subtracts out the fuel I added. I am starting to suspect my stock O2 sensor is on it's way out.

If you have a wideband, can you tell me what yours does at idle?

 

[polobai]

mine idles between 15.5-16.8 with no problems. i was concerned about the lean idle, but unless the motor is under load, it should cause no problems. if i turn up my base fuel pressure, then i can get it to stick to around 14.7, but its fine where it is now. ps-when i add fuel with my afc, the ecu corrects mine also, but not when i turn up the fuel pressure.

 

[Red Dragon]

Mine idles just like yours, high 14's low 15's. 28-30fuel psi with vac attached (Lex/550's)

 

[MK3Brent]

Before I had some major TPS issues, I would idle at 14.7:1 right on the money.

550's, lex, walbro, afpr. 38psi off vac. :nono:

 

[jdub]

Mine idles at 15.5-16.5. 30 psi on the FPR with vac attached (Lex/550's)
No issues...smooth idle at 650 rpm warm.

 

[bluepearl]

My A/F ratio at idle bounces between about 14.6 and 15.3. When it does reach the lower-15s the engine gets a little rougher and starts making the typical lean idle pop sound. I can add fuel with the S-AFC or turn up the fuel pressure, but eventually the ECU just subtracts out the fuel I added. I am starting to suspect my stock O2 sensor is on it's way out.

If you have a wideband, can you tell me what yours does at idle?

ken, mine usually is in the 14.5 area, once in a while it will bounce to the 15 area. Fuel pressure is at 40 vac disconnected. 31 with. 50m trim with the stock AFM screw all the way out. stock injectors. vf is 2.17 at idle and mostly closed loop. If you need more specs, ask Joe

 

[zurud]

mine idle at 25, when light throttle will go down to 20 and boostin to 13 psi will drop to 10. Set the pressure with vacuum off at 30 psi.

 

[paddlenbike]

ken, mine usually is in the 14.5 area, once in a while it will bounce to the 15 area. Fuel pressure is at 40 vac disconnected. 31 with. 50m trim with the stock AFM screw all the way out. stock injectors. vf is 2.17 at idle and mostly closed loop. If you need more specs, ask Joe

Same here. When it stays at 14.7:1 the idle is Lexus smooth. As soon as it goes into the low-15s at idle, you can hear the lean idle pop. Sounds like this is pretty normal but my O2 sensor has 150,000 miles on it and is probably overdue to be changed.

While checking my fuel pressure I noticed something--it's at 40-41 psi with the vacuum line on. Pull the vacuum line and there is no change. There is NO vacuum coming from the two ports on top of the throttle body or from the entire vacuum hardline that runs along the intake manifold; certainly this can't be normal. My boost gauge is tapped into the back of the throttle body and shows 19 in/hg at idle. :icon_conf

 

[bluepearl]

Ken you are on to something, check that vac out. Did you ever check you're vf at idle and/or cruise?

 

[paddlenbike]

Ken you are on to something, check that vac out. Did you ever check you're vf at idle and/or cruise?

Haven't done that yet. I sure wish these cars had OBD-II. I have a $90 OBD-II reader that I can hook up between my 4Runner's OBD-II port and either a laptop or a PDA and read all of the engine parameters (including short term and long term fuel trim). I think the Vf reading on the Supra will give me only instantaneous fuel trim and not what's happening long-term. It would sure make monitoring and tuning easier if the Supra were so-equipped.

 

[NJsupraA70]

While checking my fuel pressure I noticed something--it's at 40-41 psi with the vacuum line on. Pull the vacuum line and there is no change. There is NO vacuum coming from the two ports on top of the throttle body

Thats a problem right there. The t/b ports are used for the charcoal canister and for the egr vsv. So thats a big no-no hooking up your fpr there. You want manifold pressure post t/b. Hope that helps.



On a side note my car acts identical to yours at idle. it fluctuates between 14.7 and 15.2 at idle with base f/p set at 32 psi. I think its normal, doesnt really bother me personally.

 

[paddlenbike]

Thats a problem right there. The t/b ports are used for the charcoal canister and for the egr vsv. So thats a big no-no hooking up your fpr there. You want manifold pressure post t/b. Hope that helps.

I just started another thread after doing some more investigation. The stock FPR is hooked to the same source as the charcoal canister (BVSV) and the EGR and certainly it should see vacuum/boost.