Low Idle, Stumbling When Driving

[ram360]

So my 94 cobra developed weird issues last week. Cold start the car will fire right up and idle normal 800 rpm or so for about a minute then my idle drops to 550rpm. It's a mild H/C/I, tfs stage 1 cam. and it's just barely running at that rpm. I did the idle reset etc.. and no matter how much I open that idle screw I can't bring it up. Also now the car around 2000 rpm it starts to buck sometimes. I haven't pulled the codes (CE light has been on but it's b/c of an egr delete and I have no tune in the car to shut it off...yet). Ignition is all recently done, I did put in a bullet 75mm maf maybe that's related to the driving issue, but the idle was like that before that happened. Any input is appreciated!

 

[toyman]

First, I wouldn't assume the EGR is the only reason the CEL came on. You should pull the codes (many don't trigger a CEL) to see if the computer is logging other events. You can't effectively alter the idle by adjusting the throttle stop screw as the idle is a computer command setting. What you can do by playing with the idle stop screw is alter the TPS signal to something the computer wasn't expecting. The stock MAF signal is what the computer is expecting so any other MAF, unless it's calibrated to the injector size, is a no go.

 

[RIO5.0]

If your CEL is on due to the EGR delete just plug it back into the unit. You can disassemble plug connection from the unit, secure the plunger 1/2 way, and stash it on the firewall. Mines been off / deleted for 8 yrs this way and never throws a light. You don't need a tune to shut that off.

 

[ram360]

The MAF is calibrated for the injectors. I will put a moates QH on the car over the winter so I'm not terribly concerned with the egr. I'll take it for a run to the parts store and have it scanned to see what It comes up with and go from there. Prob the best thing to do otherwise I'll just be guessing.

 

[toyman]

Just make certain they plug into the correct data link port. It isn't the one under the dash. It's on the passenger strut tower in the engine bay.

 

[ram360]

I pulled the codes w/ a jumper wire since advanced auto is worthless and can't pull codes on anything older than 96.

Anyway

KOEO
327 : EGR circuit below minimum voltage
565 : Canister Purge Circuit Failure

KOER:
172: Heated Oxygen Sensor indicates lean condition right side
136: Heated Oxygen Sensor indicates lean condition left side
327: EGR circuit below minimum voltage

The EGR codes are self explanatory since it's not there. Highly doubtful it's a fuel issuet, maybe the new maf, or a vacc leak somewhere. I really doubt the car is lean, the exhaust smells rich as hell, although I don't have a wideband to verify and you can't really go by that smell all the time w/ newer fuels. I've heard of a bad ECT causing lean conditions but I'm not getting a code for ect voltage. Going to start w/ checking for vacc leaks. Pulled the vac hose off the intake feeding the vacc tree and bypassed all that and no improvement. Going to check the ports on the intake, some may have be unused and plug w/ vacc caps and I know the caps dry out and crack. I guess we'll see. Prob something stupid.

 

[ram360]

UPDATE: After ruling out anything after the vacc tree, since I bypassed it. I moved onto the intake ports. Sure enough the one looked fine but as soon as I touched it. I found this.

As you can see it was a craked vacc cap on one of the intake ports. I changed the lower intake gaskets a few months ago and replaced all the caps w/ the heavy thick caps and they still crack from the heat. Looks like I'm going to have to find a new way to cap these off b/c the heat is just killing these. I'll clear the codes and road test it later to see if this was the entire cause or just part of it.

 

[toyman]

Might be heat but also the caps may be too small for the tube. If they are stretched they are more likely to split as yours appears to have done.