Terrible Idle/Surging Issue... and I'm getting 9 mpg because of it T.T

Blau · Oct 11, 2013

Hey fellas!

I've been trying to fix this issue for quite some time now, but I just can't seem to get it resolved. Short background: She idles anywhere from 750-1800 rpm.. surges to 3000+ between shifts.. surges up and down from 2000 to 1000 rpm while rolling downhill in neutral.. and hangs around 2000-3000 rpm until I come to a complete stop, at which point idle returns to somewhere around 1100 (occasionally much higher). I replaced the IAC a little while back, which resolved an issue where idle would rarely ever drop below 2500 rpm. I've thoroughly cleaned the MAF and throttle body. My TPS is reading .92 volts, so that's working fine. At this point I'm wondering if it could be the EGR or PCV? My mechanic thinks the issue could lie somewhere in my throttle body, causing my throttle to stick, but as far as I can tell, everything checks out there. I'm running catless and without o2 sensors -- could putting them back in resolve this (prev. owner did the exhaust setup, so I'd have to buy a new exhaust)? My air filter is pretty old and beat up... but I don't think that could cause so much of an issue at all, could it? I pulled self test codes today, came up with quite a few codes. Some of them I'm guessing are probably from the swap (I have a '94 5.0, trans, rear, etc. inside a 2000 chassis).

327 - DPFE or EVP circuit below minimum voltage of 0.2 volts
565 - Canister purge circuit failure
176 - o2 Sensor circuit indicates system lean (left side)
556 - Fuel Pump circuit failure
172 - o2 Sensor sensor circuit indicates system lean (right side)
146 - I can't find any info on this code anywhere
411 - Cannot control rpm during KOER low RPM check
147 - driver's side (post converter?) o2 sensor

Can anyone make sense of this? I'm a bit too in over my head to know where to go from here.

CC'S95GT · Oct 11, 2013

your computer has no idea how rich or lean it's running so it's goes into open loop and the car will run rich.

The O2's need to go back in first.

The surging sounds like a vacuum leak.

ttocs · Oct 11, 2013

as he said the o2 sensors are not optional... a list of mods that have been done will be helpful. For the way its surging when you shift there is a screw on top of the throttle body that needs to be adjusted down.

Musturd · Oct 11, 2013

Who the hell removes the O2's I'm lost once I read that I stopped reading because that's obsurd

Blau · Oct 11, 2013

I had no idea not having o2 sensors was that bad! Thanks for letting me know guys. The previous owner took them out, or probably never put them back in.

GT Rob · Oct 11, 2013

Check for vacum leaks my car did almost thecsame thing and I changed almost everthing I could truned out to be the vacum hose behind my intake its on the lower intake by the firewall

ttocs · Oct 12, 2013

o2 sensors are not needed for carborated applications but in a modern fuel injected system the o2 sensors are what tells the computer if its got the air/fuel mix correct. With out them the computer is basically just guessing what too do since the ecu has no idea how I is running.

Orange 94 · Oct 12, 2013

Like the other guys said put the damn o2 sensors in!!!

The first pair you need!!
The second pair after cats are optional, they're just emission control.

CC'S95GT · Oct 12, 2013

Orange 94 said:
Like the other guys said put the damn o2 sensors in!!!

The first pair you need!!
The second pair after cats are optional, they're just emission control.

he has a 5.0 and OBD1. only 2 O2's and they're before the cats (or at least where the cats should be)

RichV · Oct 12, 2013

Blau said:
I had no idea not having o2 sensors was that bad! Thanks for letting me know guys. The previous owner took them out, or probably never put them back in.

Yea, the EFI needs those probably the most. It's like wondering why your house has no heat without a thermostat.

How long have you been driving without them? Sounds like quite the mix of unconventional parts. What EFI generation you running? I mean, there's so much custom stuff, there may be more issues hiding in the background.

ttocs · Oct 12, 2013

I am not the motor expert by any means in this post but wouldn't it be a good idea to at the very least pull a plug and see how it looks and if it needs replacing? Seems like with it operating the way it has been surging and all that it would have been easy to mess up the plugs but this is just a fairly uneducated guess which is why I am asking the experts.

Orange 94 · Oct 12, 2013

CC'S95GT said:
he has a 5.0 and OBD1. only 2 O2's and they're before the cats (or at least where the cats should be)

Right, missed the 5.0.

CC'S95GT · Oct 12, 2013

Orange 94 said:
Right, missed the 5.0.

it's all good

Blau · Oct 12, 2013

RichV said:
Yea, the EFI needs those probably the most. It's like wondering why your house has no heat without a thermostat.

How long have you been driving without them? Sounds like quite the mix of unconventional parts. What EFI generation you running? I mean, there's so much custom stuff, there may be more issues hiding in the background.

My EFI is from a 1994 -- as is essentially everything else in my car. I'm gonna pop in some o2's probably later today -- I'll give you guys an update then! In the meantime, I'm gonna start looking for a vacuum leak...