L98 350 tpi what controls idile speed/rpm?

slideways

slideways

Club Member
So i just picked up a 87 Firebird Forumula Stripper car no A/C power window or any of that its a pretty good find be she needs so work im doin the usual plugs, wires, cap, rotor, oil change all that good shit tommrow, Now the mail problme with the car (other than exhaust leaks lol) is that it idles at almsot 1600rpm and there is an inconsistant miss when at idle im guessing its a sensor of some sort but does anyone know off the top of their head what sensor woudl control idle speed?
 
well, same as most EFI cars, the IAC controls idle, but first check for a vacuum leak, as this can cause a high idle and a miss/rough running
 
OK thats what i thought i was just making sure, things are a little messy under the hood but its all stock so its not to chopped up hopefully i can figure it out tommrow thanks
 
O and if it helps any i almost forgot the car runs out of power and is very very hesitant to shift after about 4000rpm? I know its runnin on 7cyls right now (burnt plug wire) so ill get that taken care of before i worry about that more
 
slideways240sx said:
O and if it helps any i almost forgot the car runs out of power and is very very hesitant to shift after about 4000rpm? I know its runnin on 7cyls right now (burnt plug wire) so ill get that taken care of before i worry about that more
Click to expand...

Wow got some work to do. SOunds like it could have a BAD maf. But it also sounds like you either have a humoungus vacum leak or someone has dicked with the base throttle setting to get the thing to idle. First thing you need to do is to get a scan tool on that thing and see what going on data wise. With a bit of data I could render some assistance but it'll be minimal without some in depth stuff unless its really obvious and not a large vacum leak.

Some base line number to use for testing JIC you have a DVOM.

TPS 0.49 0.79 throttle closed.If higher adjust base throttle till in range.

MAF at 650 750 rpm idle should be just over 1 volt. Should repsond the throttle snaps with at least 2.5. It should also closely follow the TPS on a steady state throttle opening rate with the engine running fairl cleanly. If you see signs of Voltage dropout replace and restart the test. The Maf's on these cars very failure prone.

Check the ECT it'll do some crazy stuff to idle if its stuck cold.

check all vacum lines make sure all hole are plugged etc. If the leak isn;t obvious block of the brake booster hose. Those things are starting to leak at this age in the vehicle.

Make sure all plugs/wires are in good shape yadda yadda yadda. If you can't find it after a little bit of detective work. Bring It by the shop and I will look at it for a nominal charge.
 
Ha well since my mechanic knowladge is minimal once it get to the eletronics part im going to start with the rego tune-up and check all the vacume lines i can i did a quick overview but didnt see much, from there ill replace the IAC and if that dosent help ill look into some MAFS, if that dosent help, Well there will be another 3rd gen down and cars lol thanks alot for all the advise though
 
sorry sean no mass air flow sensor on that car.

It sounds like you have a compounding problem here.

#1. Get a good tune up in it (PLUGS, wires, cap, rotor, check the coil, and its a gm so the ignition module might be on its last leg.)

#2 as sean said Vac leak. listen around the motor for hissing or use a can of brake cleaner and spray around the intake area and if the idle changes then you have a leak.

#3 you said its all kinds of crappy on any load so check the EGR system or just delete it. That causes all kinds of hell on older 350's they get carboned up and freeze open causing too much exhaust gases to be let into the intake and it causes all kinds of shit.

#4 check the air pump, its belt driven, its probably bad. if possible get rid of it along with all the air lines that go to the exhaust manifolds, but to do that you might have to weld some holes up. AIR system is a pile of shit and does nothing useful if you do step 5.

#5 lose the cats, the older gm ones suck major ass, its old enough so even if they start emisions testing, your fine.

#6 get new O2 sensors. they are one wires on that car if i remember correctly. they are kinda sensitive and get jacked up easily so if the car has been running badly lately they are probably all carbon fouled and need to be replaced.



Im sure i could go on but do that stuff and see how that thing runs. If the above don't help then you need to get a bigger motor in that car. :D


EDIT: your idle problem is probably the IAC motor. its on the bottom side of the throttle body and its a little pintle motor. try cleaning it first but if that dont help get a new one.
 
Last edited:
MyGreenBabyZ said:
sorry sean no mass air flow sensor on that car.


#2 as sean said Vac leak. listen around the motor for hissing or use a can of brake cleaner and spray around the intake area and if the idle changes then you have a leak.
Click to expand...

keep a fire ext. handy when doing this.. trust!


MyGreenBabyZ said:
#3 you said its all kinds of crappy on any load so check the EGR system or just delete it. That causes all kinds of hell on older 350's they get carboned up and freeze open causing too much exhaust gases to be let into the intake and it causes all kinds of shit.
Click to expand...


More common than most people think.

MyGreenBabyZ said:
#6 get new O2 sensors. they are one wires on that car if i remember correctly. they are kinda sensitive and get jacked up easily so if the car has been running badly lately they are probably all carbon fouled and need to be replaced.
Click to expand...

Be carefull not to dent the case of the new hego in anyway.. this will ruin it.
 
igotaneed4speed said:
keep a fire ext. handy when doing this.. trust!





More common than most people think.



Be carefull not to dent the case of the new hego in anyway.. this will ruin it.
Click to expand...

You have a TPI formula right ?? an 87 TPI formula ??? it should be a MAF car if its a TPI formula.
 
Also, in case anyone didn't know, Sean can lay down a tune on a TPI. Not many people are doing that nowadays. i thin khis shop car with the 427 was a TPI.

-Geoff
 
You must log in or register to reply here.
Back
Top