Hi there

Heres the issue ive bought a 88 305 iroc convertible after week or so i noticed some issues, number one being cold starting. The car starts but then struggles it does not stall the rpms get really low then they rise again rapidly. After the car warms a little it settles down to around 750rpm or so. Somtimes after this warm up period the car drives fine but on most times there is low power, poor idle ,hesitation, bucking and surgeing its awful to drive at times.
So far ive replaced the plugs leads distributer cap and roter the IAC motor tps sensor egr valve and ive also replaced the injectors with a set from southbay fuel injectors the car seems smoother but the issue remains

Can you please help me with this its starting to get fustrating and expensive
Thanks agian Anthony

 

What about vacuum lines? Dry rotted lines will cause idle and running issues.
Vacuum Lines Diagrams
Does your car have a Mass Air Flow sensor?
If so, unplug it when the car is running to see if it gets worse.

 

Thanks for the reply Ive checked all the vacuum lines and they all seam leak free and in good condition my car does have a mass airflow sensor i will unplug it tommorow and see what happens

 

Did you notice if any of the hard plastic vacuum lines that run between the upper and lower parts of the TPI plenum and under your throttle body are broken or cracked?

 

Ive checked all the hard plastic lines and conections when i swapped the injectors and they all seem fine to me. Im thinking this may be a fuel supply issue sometimes when trying to start the car i put the ignition on the pump primes then on ocassion ive herd the pump priming while i crank the engine

 

check for pressure . there is a rubber line in the tank conecting the pump to the hard line that goes bad all the time , change fuel filter first .

 

I will check the fuel pressure the fuel filter has been changed also

 

EGR Solenoid ?
- hard to find. I put up an ad for a used one and got 3 offers, so I bought 2 for like $25 incase the other one was bad. Seemed to smooth mine out.

I did about the same as you
EGR Valve
EGR Solenoid
ESC
TPS
MAF
Cleaned IAC

 

It could be the egr solenoid is there any way to test it before i spend any more money

 

This is the advice I was given ...

The valve is opened by vacuum that comes from the solenoid. The computer runs the solenoid and looks for the switch position to tell it if the valve is open or closed. It looks at the switch at startup. If the switch is closed, meaning that EGR is flowing, it will put on the ses light. This could be caused by a bad switch that is closed all the time. Or by a bad solenoid that isn't shutting off vacuum. Or by a valve stuck in the open position. Any of these can be intermittent as well. That's why I said check for vacuum from the solenoid going to the valve. At idle there should be very little vacuum on the hose to the valve. The solenoid will leak a little bit but not much. The standard test is to put your finger in the valve and have someone rev the engine to 2000 rpm and check for valve movement. It should move as you get off idle. I'm talking about putting your finger under the mushroom top of the valve and feeling the diaphragm move up and down. I don't think you can do that with a tpi. Maybe a long thin screw driver? Possibly if you bent it into a fish hook shape? That gives you an operational test of all the components. This is why I always use GM parts. I've replaced too many napa and other company's parts just to find them bad. Hope this helps.

 

Jersey89GtA thanks for the detailed advice i will try all those methods when i next go to the car over the weekend (i keep it in a friends garage) im leaning towards the egr solenoid i went round my engine with a large screwdriver listening to various parts and i listened to the egr valve at idle and it sounded like it was flowing to me. Ive read that it should not be that open at idle speeds theres never been a ses light turned on on start up wich i thought was strange given how rough it starts. I always use gm parts too ive always used genuine parts on all my cars the non gen stuff is junk in my eyes. Btw i get all my parts from rock auto with me being in the UK and the sell delco egr solenoids for around £18.00

 

Replace the IACV (NOT CLEAN) and the CTS on the front of the block above the Waterpump.. That sensor has a tendacy to make the car act stupid and doesn't usually spit out any computer codes..

CTS = Coolant Temp Sensor / You said "Car runs better when warm"
IACV=Idle Air Control vavle / Forces Higher idle at low RPM

 

Hello ibmtech ive replaced both the IAC and the CTS with no change to the problem

 

HMMmm... ibmtech, thanks I will try the same. Love this forum, learn alot.

I only cleaned my IAC and did not change out the CTS.


I run pretty smooth, but on cold starts I get the SES light code 32 egr, I get engine hot, restart - light goes out, idles up to 2000 and imeediately lowers ..... CTS and IAC must be screwy.

 

Right sorry guys its been a while i've been busy with work and things ! First off i have checked the fuel pressure and it holds steady at about 40 psi. I got the code 33 from the computer we have changed the maf sensor maf relay and burn relay the car performs better but its still not 100% the car will not run with the maf unplugged i remember my old iroc would run with the maff unplugged i'm thinking either its the wiring or a possible ecm problem food for thought anyways cheers Ant

 

"Originally Posted by thetemplar
Hi there
Heres the issue ive bought a 88 305 iroc convertible after week or so i noticed some issues, number one being cold starting. The car starts but then struggles it does not stall the rpms get really low then they rise again rapidly. After the car warms a little it settles down to around 750rpm or so. Somtimes after this warm up period the car drives fine but on most times there is low power, poor idle ,hesitation, bucking and surgeing its awful to drive at times."

Nothing like bringing up an old thread but my 305 is doing the same thing. Did you get your problem resolved? I just ordered a coolant temp sensor and the IACV. Hopefully that fixes it. I did replace a lot of relay wiring connectors that were rotted out. Maybe I have a bad relay also.

Thanks

 

ECT sens or wiring is a possible cause. This would also likely cause poor running when the engine is warm. A faulty sensor or connection is just as likely to be faulty with the engine warm. Make sure the EGR isn't stuck open. To correct something that was posted above, the EGR solenoid is connected to ported vacuum. The solenoid prevents the valve from opening at all until the engine is warmed up, or at any time the ECM disables EGR. With the solenoid turned on, the solenoid is closed and no vacuum should get through it. If the vacuum lines are connected right, there will never be vacuum to the EGR at closed throttle. Plus, the EGR on these cars is a negative pressure modulated design that further prevents it from opening at idle. If the valve is stuck open, you can pull it and try cleaning it. Check it for a failed spring. Generally though, a failed EGR spring on a pressure modulated valve will not cause the valve to be open at idle but rather to open too quickly on throttle tip in and produce a slight buck jerk at very low speed.

If the engine runs poorly only when cold, check for vacuum leaks that will make the engine run lean in open loop. These systems run in open loop until the engine reaches about 120 degrees coolant temp and the O2 sensor warms up enough to begin reading. On single wire sensors, this usually doesn't happen until the car is driven some. In open loop, the ECM will provide some fuel correction by Block Learn long term correction. Short term Integrator correction doesn't come on until closed loop. To check for vacuum leaks, you can use propane or Brake Cleaner sprayed around the manifold seams and hoses, listening for a response from the engine at idle. If you have a scan tool that is compatible with GM OBDI, you could use it to monitor data while you spray the intake and look for 02 sensor voltage to spike high. Again, the O2 sensor has to be heated up for it to respond to added fuel. The engine will still respond though. How is the state of tune? Plugs, wires cap and rotor, timing. Check fuel pressure after cold start. Be sure the pump isn't weak and the filter isn't plugged. Of course fuel supply should affect it more under load while driving. There's more to look at. Check these things and post back. Best to start your own thread so you get more attention.