Hi all, great site
I searched and really didn't find an answer to the problem I am having. I recently rebuilt my 350. It has less then 600 miles on it. The car has a surging idle. When the auto trans is in park the idle is terrible. When the trans is in drive it smooths out. The idle problem is not so noticeable when the engine is first being warmed up, but as soon as the fast idle stops it gets worse. I have replaced the following: plugs, wires, cap, rotor, fuel pump, fuel filter & sock, coil, egr vacuum solenoid, map sensor, coolant temp sensor, coil pigtails, cts pig tail, tps pig tail. I have checked the egr on and off the vehicle. I have checked the voltages at the map connector, the tps and egr solenoid. All are ok. The tps and base idle were set. The iac was removed and looked good. The iac had been replaced about 4000 miles ago. I have been over the manifold several times looking for vacuum leaks and only found one which I repaired. I even replaced the tbi gasket again to be sure of it. All of the vacuum hoses were replaced. I checked the vacuum with a gauge and it holds steady at idle. I checked the injector pattern & both injectors looked pretty much the same. One had just a tad wider pattern. The spray pattern on both didn't look as fine as I thought they would. Not sure what would be correct. I had the TBI rebushed and blue printed about 4000 miles ago. The service engine light has not come on and there are no codes stored. The car runs good on the road.
I had a Ca pre smog check done and it failed with a high NO. It was just over the limit. The smog tech suggested the cat be replaced and I did so. I am trying to resolve this idle problem before I return to get the smog checked again.

At this point I am about ready to pull what is left of my hair out. I don't have access to a laptop and a cable. Does anyone have a picture of what a good TBI injector spray pattern should look like? Could the problem be the ignition control module in the dizzy? I don't know what else to check.

Thanks any suggestion or advise would be much appreciated!
Brad

 

I think there are two different TBI base gaskets. Maybe only true for 7.4L ? If you have the wrong gasket it leaks under IAC. TBI spray should be conical and same on both sides. I believe they can professionally cleaned. when returned to you use the simple gasket kit to reinstall.

350 CID? A truck?

 

Thanks I will check out the gasket. I am trying to locate someone locally to clean the injectors and check them out.
Brad

 

I wonder how they clean them? ultrasonic? maybe just exchange for cleaned ones?

 

I haven't found anywhere locally that does them yet. I did find this place and they explain what they do. I may have to send mine to them. Here is their cleaning process.

http://www.witchhunter.com/process2.php4

 

very nice! looks like a thorough job.

 

I had the same issue. I assume you originally had a 350TBI and just rebuilt that. Correct? Did you do a stock build or did you upgrade the cam, heads, intake, etc???

Check your timing. Check the fuel pressure. My issue was fuel pressure and it needed some tuning with the chip. Also, with a rebuilt TBI you should check the injector filters. The one on the side of the injector (very tiny) and the lower injector filter as well. Some metal fragments/dust may collect there if the TBI was not cleaned out after the rebuild. I have seen this before.

You have done a great job at being very thorough. At this point it is usually something simple/basic, but is no less frustrating, lol. Where are you from?

 

This is not the best picture. Kind of hard to show the spray pattern, but the most important thing is that they look equal.

If you need the lower injector filters and the smaller ones let me know. I will send you a couple of each. Just pay the shipping. The only way to get those filters is with a $25-$35 kit at your local parts store. No need to spend that kind of money on those.