1998 discovery issues, Part 2
 

OK, I have checked fuel pressure, ok. Check firing order and all plugs, ok. Cleaned throttle body, checked connections to TPS, MAF, Coolant sender, etc. Checked hose to regulator, ok. The only current code is P1191. Now the vehicle still runs rich with the 3prong, aev plug connected to the pump. Without, it idles around 2k. R&I'd the TPS, no change. Left TPS out, no change. Then for grins, disconnected the MAF sensor, it stumbled, then resumed on its' elevated idle. Continued to run at 2000rpm. Continued to respond to accelerator without the MAF connected. I am at a loss. Any help out there? Please......:mad::eek::confused:I have since got a fuel pressure tester, 34-38psi, rising as rpms increase. I have checked all linkage, the throttle is returning to it's stop. Still idling around 1750. When gas is applied to 2750 it will surge every 2 seconds or so to 3ooo and return. Current codes are P1447, evap purge(just replaced)still throwing code. P1191 O2 heater circuit open downstream, and P0451, Fuel tank pressure sensor fault.

I had this problem once, and what had happened was the cable adjuster for the throttle cable had popped out of its hole in the bracket on the intake and was sitting a 1/4 inch further our from the bracket than it was supposed to,

I also had an issue once where some corrosion on the cruise control linkage was holding the throttle open just a tad, but it was enough to cause a high idle

Also check the idle air control stepper motor and ensure is not being held open by a chunk of carbon or somthing.

If scanner available, check coolant reading and TPS percent readings at OBDII port. Coolant temp to ECU is separate from the gauge. Coolant temp should begin as ambient and rise, not stay at -40 (wire off). TPS should be around 9 percent at idle, rise as pedal is moved.

Make sure you check both of these possible causes.