a car I sold someone a while ago developed a symptom where it has a very poor idle or cant hold its idle. It opens right up around 4000rpm and has good power and runs well.



He had taken it to a shop and they told him one of the injectors were not grounded.



I happen to run into him and when he mentioned this to me I told him to bring it by so I can check it out.

It comes in and all the belts are loose, and it has a rather large exaust leak which sounds like its coming either from the cat or right

at the manifold.



He had some denso plugs which I swapped out for NGKs, did not make much of a difference, after trying to adjust the TPS by feel I decided to try another TPS I had sitting, it got a tiny bit better, I adjusted that one for a little bit and gave up on it for the day.



Any ideas what could be causing this? Im trying to help the guy out because the injector ground theory sounded a little crazy to me.

Injectors not grounded? Thats because the are pull to ground circuits:)... With idle symptoms and low speed issues, I always start with a compression test, before wasting alot of time with further diagnostics.

Try setting the idle mixture with the initial set connector jumpered, then set the idle speed.

if its an S4 there is freeze plug on the block between the intake and exhaust manifold, if it pops out its an exhaust leak. you can see it without taking anything apart

that exaust leak will cause the car not to run properly?



it is a S4 NA

max- what gets me is the car was running great, then he got this

no, do what maxt says for the running bit. i answered the noise bit

Run a code check on it just to make sure all the sensors are reading.. any evidence of the cas moving at all? its so hard to trouble shoot stuff over the wire without actually hearing the car, so basically you have to just start following down the troubleshooting path.

I always just do a quick compression check just to see where I am headed. Then its usual, all sensors plugged in , all sensors reading, any vac tubes broken, then from there, its where you have to really start testing stuff like injectors, ignition coils wires etc..

You can get wierd stuff to like like only one leading coil post firing, Bad ecu's and junk like that.

The error codes are on teamfc3s for the s4.

ill feel bad if it turns into a big problem for him

So it runs fine in the secondary injector RPM range? Seems like the primaries acting up.

more likely to be an internal engine thing, or a vacuum leak imo