i have 87 iroc 5.7 tpi. idle drops down like the car is going to shut off but when the idle gets low it jumps back to normal. put tps senser,idle air control valve,still doing the same any ideas

Have you cleaned the throttle body? Sometimes crud
gets built up on the backside of the throttle plate.

yea i tried that

hmmm check the mass airflow sensor.

is there any way of checking the m.a.s besides replacing it?

any way of checking the m.a.s

Is it throwing any codes(check engine light)? How about the 02 sensor? I remember diagnosing the mass air sensor in my Grand National by tapping it with the but end of a screwdriver and seeing if there were any changes in idle. Do you have a voltmeter? Also, you can take a look inside the MAS and check the condition of the heatwire.-----Scott

The MAF has a lead that should vary between 0 and 5 volts when the air flow changes. A common problem with that year is the connector pins on the MAF get sprung out of whack and don't make good connection with the MAF. If you measure the voltage it will be 5 volts all the time. Try disconnecting the MAF and gently criming the socket pins so they grab the MAF pins better and see if that helps. But if this was the problem, I'd expect you to have a check engine light illuminated. Do you? If so, get the codes and see what they say. There are several things that can make you idle misbehave as it is.

thanks 4 the info guys, but the big problem is that the car has had the smog pump and cat removed plus some wires disconnected and the check engine light removed.besides just the bulb.so my code scanner is useless.butt today i found out that the i.a.c.v has to be adjusted i did not do that when i replaced it so i will try that right now and see if that works

??? so with all that stuff removed ??????
you didnt say that to begin with?
cmon of course the OBDII isnt gonna work right so hence bad idle.
jeez!

No OBDII on a 1987(started in 1996). But dawg is right. You can`t gut a FI car like that and expect it to run right. What other wires were disconnected. Sheesh, why don`t you just strip everything and throw an intake and carb on there. As an aside; very sweet ride there dawg. Are those Welds , and if so , what size?-----Scott

well i adjusted the i.a.c.v and that did not work the car ran great when i first got it. woever did the work knew wat to do.it has a superchip,zz4 crate engine with the tpi setup,airfoil,and some accel upgrades i found this out myself.no emissions,lots of power.after few months i stop at store came out i notice the problem right away.i bought a book on fuel ejection and seen this little senser that goes on the intake called manifold air temp senser book sais it works with the e.g.r and can cause poor idle,so thats on tomorrows list ill post back if thats the problem.

FWIW, the TPI setup at least uses a quasi PID algorithm in the idle feedback loop. With any feedback loop, so long as the system's response remains unchanged, the feedback algorithms response will not need to be adjusted. But if the system's characteristics change, you can get an oscillation in the feedback loop that causes the idle to surge.

The inputs to this feedback system are the Mass Air Flow (MAF) sensor, and the engine RPMs. Indirectly, timing affects the control loop because it has a drastic affect on engine RPMs. The Mass Air Temperature is also an input, but it is such a slow reponding loop that it's doubtful it will cause surging.

Some things that can cause your engine's control response to change are things that affect breathability of the motor. An updated set of heads or cam can cause it when the stock chip is used. If the MAF sensor fails to read air flow accurately the same problem can result.

Examples of MAF problems are a leaky air duct between the sensor and throttle body. For that matter, an air leak anywhere can be at fault including the EGR valve, intake, or PCV system.

The PCV hose can connect to one of two similar ports on the drivers side of the engine. If it gets connected to the wrong port, this problem can occurr. The PCV system is essentially a controlled leak which the ECM is programmed to account for. If this leak changes significantly, it can cause the system to oscillate.

I believe your engine has a fully electronic HEI system on it without mechanical or vacuum advance. Try backing off the timing a fuzz and see if things improve. Check to ensure the harmonic balancer's TDC mark is really at 0* using a piston stop. If it works, consider tweaking the timing map within the PROM.

You'll probably find the Third Gen (http://www.thirdgen.org) web site usefull. Someone there may have some other useful advice since your problem is not uncommon for the TPI motor. There is also lots of info on PROM burning and tweaking which may or may not be your cup of tea.