Morning,

I finally got my motor running but I seem to have inherited a problem from the old owner of the motor. ( he was having the same problem)

The Problem:

The motor starts and will idle at 1000 to 1050 cold or hot.

Motor Specs:

1989 305 TBI
Turbo city TBI unit.
Matched injectors
No smog(removed)
Reprogrammed computer to reflect the removed smog equipment(reprogrammed by affordable efi)
Injector spacer
TBI unit spacer
Stock Dist.
New Plugs, Wire, Cap rotor
Timing set at 6 degrees.
No knock sensor(wasnt included in the after market harness.)
All TBI sensors except the knock are installed
O2 is on the drivers side exhaust pipe about 2 inches from the collector

What has been done so far:

The PO had backed the Idle adjustment screw all the way out so it wasnt resting on the throttle linkage. I had to adjust this up just a hair because it was allowing the throttle plates to stick. Idle didnt change.

I put my scanner on to get some readings. all spec ranges are taken from chiltons manual but I forgot my scanner at home to pull the readings from it.

TPS is within spec.
IAC was disconnected by jumping the a and b ports and then disconnecting it.
Scanner indicates it is in closed loop mode
Smells rich
MAP sensor is within spec
Coolant sensor is in sync with my gauge (open radiator is at 180/190 range, covered radiator temp goes to 210 both on gauge and sensor
All vaccum lines are new, only one line which is the map sensor coming off the back of the TBI unit. The rest are plugged.
Checked for vaccum leaks with propane and idle remained the same.
I disconnected one injector but I did'nt run it long enough to get the Rpm readings (I will tonight)
O2 sensor is within spec.


Things I am leaning towards.

1. I am thinking about getting or making an ADAL cable and software to double check things software wise.
2. I am picking up a tbi gasket kit tonight to reseal the TBI unit.
3. If all that fails I am going to pick up a stock TBI unit and bolt that up.

Any suggestions on things to check or what might possibly be the problem would be greatly appreciated.

Thanks
Steve Piazza

 

Honestly, that is not a high idle assuming your tach is even accurate. High idle IMO is 1500 RPM and up. When I got my 92 a little over a year ago it was idling at 2000 RPM because the minimum air set screw had been tampered with.

Some cars need to idle at around 1000. I know my 88 305 TBI with a cam did and my 92 does as well.

 

Sorry I should have mentioned.

This is a stock motor, except the tbi unit.

Manual as well.

 

Manuals idle higher than automatics do and you also have your timing advanced 6*. Is the TBI one that flows more over a factory unit or just one of their rebuilds?

 

I am not 100% sure but the TBI unit it self is stamped turbo city so I am assuming it is one that will flow more air.

Is there a way to check?

And I agree that sticks idle higher the autos but when factory settings are saying 500 to 650, and its idling at 1050 more or less this isnt exactly right.

 

Are you basing your rpm readings off the stock tach or an external tach? The stock tach in notorious for being off.

 

I didnt specifiy? sorry about that.

RPM readings are coming off the computer via the scanner and my Autometer Tach.

 

Just to keep an update incase someone finds it interesting.

Ok rebuilt the TBI unit last night. No change.

But I did notice a few things.

1. the TBI unit is an upgraded high flow unit from Turbo city with a 48mm bore and upgrade injectors.

Figure stock the motors Hp is 170 to 195hp

IF I do a search on flow rates and injectors I am looking at a range of

88 to 128lbs/hr based on hp and 2 injectors

The upgraded injectors are rated at

99 on high flow, 90 on low and 95 average.

according to turbo city they flow 55 an hour so x2 is 110lbs/hr

I also noticed an adjustable fuel pressure regulator, I did change this out to a non adjustable stock unit, which did help. I didn't let it get to op temp but at 150 operating range it idled at 1050.

So tonight I am going to swap out the injectors to some stock units I have and see if that fixes the idle problem. If not I will throw the stock TBI unit on and see if it idles at 650 to 700.

 

One thing to look out for is the modified chip in your ECM probably has a different BPW constant setting to account for the different sized injectors and possible fuel pressure difference, or at least is should have had this change. This is the parameter that sets the overall fuel flow rate and needs to be matched to the injector size, engine size and fuel pressure.

Without knowing if this has been changed or not you're pretty much flying blind by swapping the injectors around and changing the fuel pressure. The chip can be read and then viewed using TunerPro if you have access to a chip burner/reader. If you still have the stock chip you could put that back with the stock injectors and see how the engine runs, I'd set the fuel pressure back to the stock 12psi also for this test.

Paul T.

 

Thanks Paul. I am sure the computer was burned for a stock 305 program.

IF all this doesnt fix it, I am going to get an aldl cable and read the settings being delivered and send it to the guy who burned the orginal chip.


Ste

 

I have a hunch it's your TBI. A higher flow unit is going to flow more air. IMO, your IAC is probably still letting in the same amount of air as it did for your stock TBI unit.

I would keep the high flow version on and play with the tune.

 

1000 RPM isn't a high idle, mine idles around 1500! When you put it into gear does the RPM lower to around 800-1000RPM? That is about right for a L03 stock.

 

A stock L03 when warmed up should idle around 675 rpm in park and around 500 rpm in drive. The ECM adjusts the IAC and fueling to hit these numbers.

If your engines are idling more than that then something is wrong with them or they have been modified. The best way to find out is to put a scanner program on them and see what the ECM says is going on.

Paul T.

 

I agree. My car is bone stock, and fully warmed up it idles right around 500-600 depending on what acc. are on like Headlights, radio, rear defrost all affect the idle. But never higher than 600 or 650.

Another thing you might check, is the engine CTS. If for some reason the ECM sees an innacurately cold temp, it will assume the car isnt warmed up yet and keep a high idle. Also will pour fuel in, thinking it is still just warming up.

 

Just to add an update.

I finally found the application for my spare set of injectors, they are off a 350tbi.

So 48mm tbi unit, with 350 injectors idles the same as it did with the green code injectors and the 48mm tbi unit.

I swapped out the larger throttle body and put on the stock one, stock injectors, stock bore 44mm. idled at 1000 till warm then dropped to 750.

Same IAC, Same TPS, Same Map, Same fuel pump,.

If i wanted to adjust things right I would have to get an ALDL cable run the scan on it and have a chip burned to the mapping of the fuel and air. Its just letting in to much fuel and air to have a nice idle. Just for giggles I may swap out the 44mm bore unit for the 48 with the stock injectors to see how it runs but more then likely I am just going to put in the injector spacer and call it good.

Steve