multiple codes and running terrible

I have a 1998 gtp and i have replaced many things including plugs, wires,maf,crankshaft position sensor,and probably a few other things i am forgetting right now. These are the codes i got with my scanner.0140oxygen sensor circuit no activity detected downstream sensor. 0300 random multiple misfire detected. 0717 input speed sensor circuit no signal.And i got 0717p,0140p,and 0300p. I parked it a couple years ago after getting tired of working on it and bought a gxp but i have to get it fixed now since my daughter just turned 16. It misses and runs very rough. I cant get the rpms over 4000. I think code 717 is the vehicle speed sensor after some research and the speedo going haywire. But i am not sure about the others.After reading some other threads I am thinking an intake gasket may be bad but i am not sure. Any ideas would be greatly appreciated. Thank you

First place to start is fix the misfire......probably needs plugs and wires......need to check coil output.......might as well change air and fuel filters and pcv, too....

P0140.....could be bad O2 sensor, bad wiring to it, or a bad cat.....running the vehicle with a misfire can damage the cat.....may be too late....

P0717 is not related to the other two problems........could be the sensor or the wiring to it....

a bunch of different problems here. check all of your power and ground contacts. even those inside of the fuse box. it is hard to tell where to start. you said you replaced the crankshaft position sensor so that is eliminated unless you received a faulty one. When did you replace all of that stuff. and when you did was there any difference in drivability after those parts were put on? may be a faulty pcm??????

After rereading your post, I'm not sure where the PCM is on your year vehicle.....but if it is in the air box, check the wiring to it for rodent damage.....

yeah it is in the airbox on that generation also.

All the parts i replaced i did a couple years ago before i parked it. And after i replaced the parts it didnt make any difference. I also went to a junkyard and swapped out the tps,and pcm but that didnt make a difference. The pcm is in the air box. Another thing I forgot is that there is and exhaust leak and you can hear it as well as smell it. Could the cat being plugged make the exhaust leak worse? I think it is plugged because i ran it for quite a while when it wasnt running right. Thanks for the ideas. I am going to start checking some things this weekend. I will let you know what i find.

depends where the exhaust leak is. if it is before the cat it can definately cause issues, along with various codes. hold the tailpipes closed and see if there is pressure there. A clogged cat will cause many problems due to the amount of the backpressure caused.

I will check that first. Thanks for replying so fast.

So I have eliminated all of the codes and got new ones. I had a bad plug wire and i replaced it and the speed sensor too. But the rpm's haven't gone over 4000 yet. It was running better for a little bit and now I am getting these codes 102 maf circuit low input and 1676 evap emission control system, purge valve solenoid control circuit. I cleaned the maf and it didnt make a difference, but i'll keep cleaning it until I get so tired of it I'll pay to get a new one.

Are you saying RPMs won't go over 4000 rpms in neutral/park or while accelerating? With the new MAF sensor DTC get it replaced. Cleaning won't help if it is electrically bad. Poor acceleration and not going over 4K rpms is a classic MAF issue.

Also, depending on your year GP since MAFs are different you can try disconnecting the MAF and see if acceleration improves or you can get over 4K rpms. The idle will be erratic until the engine warms up but OK while troubleshooting.

The rpm's won't go over 4000 when accelerating. I have disconnected the maf and it didn't make a difference. The other thing I forgot to mention is that there is an exhaust leak. And I saw some other posts that said an exhaust leak can effect the way the maf sensor works too.

The other thing I forgot to mention is that there is an exhaust leak. And I saw some other posts that said an exhaust leak can effect the way the maf sensor works too.

Where is the exhaust leak? The P0102 DTC is unique to a MAF sensor internal problem and an exhaust leak will not affect it or cause the MAF sensor to set a DTC. Your MAF is operating below 1200 HZ on the low end. The low threshold is 1500 HZ. Therefore the DTC sets.

Exhaust leaks would tend to affect the Bank 1 front O2 sensor or cause a short/long term fuel trim issue. Also, possibly the Bank 1 rear O2 sensor that monitors CAT converter efficiency.

I replaced the maf sensor and it didn't help at all. And I am still getting the same codes (102,1676) after I cleared them. Any more ideas?