1990 Cobra Idling Erratically

[JD1964]

I see in the pictures that you have a breather in the valve cover. There's supposed to be a hose from the valve cover to the throttle body. Instead you have this breather and you have the connection at the throttle body plugged. This can create problems. What you are doing by using the breather is allowing air to be ingested that is not being measured by the MAF. The pcv system takes in enough air to throw things off if it's not included in the MAF measurement. It will mess up A/F mixture.

Loose the valve cover breather and put the hose / pipe back in between the valve cover and throttle body where it belongs. Double and triple check all vacuum lines and connections. Make sure there are no leaks and all connections are tight. Believe it or not, even small leaks can cause problems. But in your case, you already have a big leak. Basically, not having the MAF measuring the pcv air ingestion is a huge leak as far as the ECU is concerned.

 

[Whitecobrafox13]

I see in the pictures that you have a breather in the valve cover. There's supposed to be a hose from the valve cover to the throttle body. Instead you have this breather and you have the connection at the throttle body plugged. This can create problems. What you are doing by using the breather is allowing air to be ingested that is not being measured by the MAF. The pcv system takes in enough air to throw things off if it's not included in the MAF measurement. It will mess up A/F mixture.

Loose the valve cover breather and put the hose / pipe back in between the valve cover and throttle body where it belongs. Double and triple check all vacuum lines and connections. Make sure there are no leaks and all connections are tight. Believe it or not, even small leaks can cause problems. But in your case, you already have a big leak. Basically, not having the MAF measuring the pcv air ingestion is a huge leak as far as the ECU is concerned.

Will do.

 

[Whitecobrafox13]

Also will be getting rid of this upper and lower tomorrow or the next day and installing my new Holley systemax upper and lower.

 

[JD1964]

As for checking fuel pressure, are you checking it with the vacuum line unhooked at the regulator? That's the right way. Set at 39psi with vacuum line disconnected at regulator.

 

[Whitecobrafox13]

As for checking fuel pressure, are you checking it with the vacuum line unhooked at the regulator? That's the right way. Set at 39psi with vacuum line disconnected at regulator.

I was reading it off the gauge in the car. 49 Psi on prime. Regulator still hooked up.

 

[JD1964]

Should be 39 psi with engine running and vacuum line disconnected at reg. Obviously reconnect vac line after setting pressure

 

[Whitecobrafox13]

Should be 39 psi with engine running and vacuum line disconnected at reg. Obviously reconnect vac line after setting pressure

Will set Tommorow. Thanks so much

 

[General karthief]

Also will be getting rid of this upper and lower tomorrow or the next day and installing my new Holley systemax upper and lower.

I would keep that cobra intake on there at least untill you got the bugs worked out. Most times adding modifications makes the problems harder to fix, besides that intake is better suited to stock engine, even if it is a knock off cobra intake.

 

[Mustang5L5]

I agree leave the Cobra on there for now unless you suspect a major vac leak


And Fuel pressure vac off should be 39psi

 

[Blown88GT]

Why does the title of this thread say 1990 Cobra?
Ford never made a 1990 Cobra, they did make a 1993 Cobra.
Putting a Cobra intake on a Fox body doesn't make it a Cobra.

 

[General karthief]

I think it was the Canadians that started that confusion, my insurance card says my 89 gt is a cobra, had a long discussion with them about it, he also may have been told by the previous owner and may not know better, not a big deal,
I hope he keeps us up on what he finds his fix.

 

[Whitecobrafox13]

Just has all the cobra pieces. Might as well call it one. And since repairing the grounds and new tps and fuel pressure adjusted to 39 Psi line off. She runs like a top. So figured its time to start adding go fast parts

 

[Mustang5L5]

Just has all the cobra pieces. Might as well call it one.

Except it's not, and I only say this because it may cause issues with troubleshooting. For instance, I see it has 19# injectors, so if you call it a cobra I'm going to assume it has the X3W ECU and matching MAF and that's why it's running like junk as true Cobras run 24# injectors. Also being an AOD to T5 swap, there are various harnesses that need to be changed out to work properly.

So really for the sake of troubleshooting, you can't call it that. For the sake of what it looks like, call it whatever you want