early fuel cut and idle bounce

[mathipa]

91' GS turbo, bone stock. had this problem for a little while now, and i dunno what else to do.

Upon turning car on, idle surges around between 1000 and 1500RPM. In neutral, if i give it throttle itll run up to about 4000, and then not rev up any higher.

in all gears, virtually any throttle bogs the car down, probably before the turbo begins to spool significantly.

its definitely putting way too much fuel in for how much air its getting, but i cant figure out where the problem is coming from. first shop i took it to, i was told the wastegate was releasing too early, so i hopped off and got that replaced. no dice on fixing it. checked for leakage as best i could, putting the tubing that flows pressurized air and the intercooler under water to check for any holes, didnt find any.

anyone got any ideas?

 

[ivanr4g63]

Sounds like your ISC is bad and may need replacing, very common for our cars considering they are over 15 years old.

try reading this link and see if you identify your issue with whats posted there.
http://www.dsm.org/how-tos/tttt/tttt3.html

Or try looking it up at http://www.vfaq.com/index-main.html

Good luck.

 

[mathipa]

the idle bounce appears to have been a leaking tube after the blowoff valve. got that taken care of.

unfortunately, still having the troubles with a bogging down engine as soon as the turbo starts to spool, though. cant get past 4000rpm in neutral, and cant get any power out of the engine at all while driving. any ideas?

 

[mephist0]

have you checked for boost leaks??? the spark plugs, the spark plug wires? and the alternator?

 

[mathipa]

plug, plug wires, alternator all checked/replaced recently.

waiting on car to cool down right now for the boost leak check, just put the tester together a few minutes ago.

edit: just hooked up the tester and checked it out, one leak at the throttle body adjustment screw. it's gonna be a few days before i can get another one...think thats it?

 

[oldman]

..think thats it?

You think so?

Are you GST or GS turbo? How much pressure were you able to register on your boost gauge during the leak test?

 

[mathipa]

ah, didnt get a look at the gauge. it was basically just me and a bike pump =p

i gotta run down to the gas station and hook it up to the air line down there and check it out, but im stuck doin yard work for most of the day.

ill drop an edit when i find out the pressure its holding, but god only knows when im gonna be able to get a new screw to stick in there to find out if thats the only leak.

 

[oldman]

ah, didnt get a look at the gauge. it was basically just me and a bike pump =p

i gotta run down to the gas station and hook it up to the air line down there and check it out, but im stuck doin yard work for most of the day.

ill drop an edit when i find out the pressure its holding, but god only knows when im gonna be able to get a new screw to stick in there to find out if thats the only leak.

No need to check, I can assure you that you would be lucky if it registers anything at all because you're at the beginning 5% stage of a typical boost leak test, using the pump at the gas station is also inaccurate because the regulator is set way too high. This is what I've posted in the past which contains the proper methods and acceptable final conditions of a BLT.

1. Disable your mbc.

2. Turn your motor to 30* ATDC to avoid valve overlap.

3. Start your test at the TB elbow and focus on area behind the TB first.

4. Spray soapy water at TB gasket, BISS, TB shaft on both sides, IM gasket, injector insulators, brake booster, afpr and all vacuum lines/connections.

5. Open your oil cap and listen for leaks. (PCV, valve seals/guide, rings)

5. Listen to your tailpipe for leaks. (EGR, valve overlap, jumped timing, bent/unseated valves)

6. Once all leaks are fixed, move the tester back to the turbo inlet.

7. Spray down the compressor cover (known leak), BOV return/flange (DO NOT TAP YOUR BOV LINE FOR YOUR MBC!!!), IC end tank/fins and all connections. Re- test.

8. Note that you will leak air into the crankcase through the turbo seal but do not panic, this is normal during a static pressure test as long as there are no shaft play.

The desired test result from the begining of the LICP (bypassing turbo) is around 20psi (on boost gauge) with the compressor set at 30psi, while taking no less than 30 seconds to bleed down to 0.

As a reference, my last test on my 500 mile new engine, I was able to pressurize the system to 25psi, bled down to about 16psi (my 1G bov) in about 30seconds, then took about 3 mins to 6psi and just kinda lingered there for a while. It's not easy to do but the point is it's possible. My next goal is 30psi After motor break in and Dodge modding my BOV. A boost leak test is one of most pita but important regular maintenace task, the key is patience and endurance, have fun.

 

[mathipa]

looking over that post, i would agree with the last sentence. once i get a proper screw in that throttle body, god willing ill be able to look over the rest.