9x8

I'm experiencing some slight pinging when the car is at idle after I give it some gas - if I press the pedal quicker and further - the more chances for detonation to occur. It doesnt seem to ping at all when at higher RPMs. The problem is also intermittent: it doesn't happen all the time and so far I failed to determine how to reproduce it with 100% acuracy.
Any ideas of what might be causing it? May it be old/bad distributor?
Also, the car seems to have excessive fuel tank pressure on hot days: that indicates a problem with tank ventilation system, right? May these two problems be linked? Where to look for likely failures?

The car is '92 euro spec on stick, I'm filling it with 98 RON octane gas as per manual.
Also, it has 152K km on odometer: around 95k miles.
It's about to be sold and I'd like to fix the problem before selling it.

Thanks in advance for any advices and apologies for my english.

[EDIT:] replacing fuel pump check valve fixed the problem.

RajDatta

One of the causes of pinging can be either bad gas or too much carbon deposits, which can increase your static compression. Was the car always run without high octane gas?
Do you always fill it up from the same gas station? Is it always the same brand gas?
Raj

9x8

Tried different gas stations, always used 98 RON: same results. Also, it doesn't seem to be dependant on gas: today it doesn't ping, tomorrow it does, even if I didn't fill up in between.

968workaholic

Sounds like you may have a fuel delivery problem or slow reaction to throttle input. A few things to consider would be dirty injectors, dirty MAF or clogged fuel filter. Once things get going its fine but the initial start is what the problem is. Do you have access to a tailpape a/f meter? That would be the best way to verify if it in fact going lean or maybe a misfire. Either way it will give you some good info.

9x8

I guess dirty injectors or clogged fuel filter are primary suspects atm.
MAF looks okay'ish.
I have no idea when the filter was replaced, so I just ordered one.

9x8

Indeed, after pressing the gas pedal, RPM actually drop some due to this detonation/misfire and only then go up. But it doesnt happen always, sometimes it runs just okay.
May the bad distributor rotor/cap cause such symptoms? They surely look old enough.

Replaced the fuel filter today, but didn't drive enough to understand whether it's better now or not. It seems better, but I'm not sure at all. I can definitely say that it didn't fix the problem completely tho.
The weird part is, if the car is shut down and then restarted after 3-5 mins of sitting, it seems to behave better somewhat for a while (throttle response is way better, it revs up right after pressing the pedal).

FRporscheman

My '93 does this as well, it's persistent though. I have already had the injectors cleaned, installed a new fuel filter, and cleaned the maf (in that order) with little effect. I don't know if my problem is the same as yours but maybe this info helps.

9x8

I think I have a suspect here.
It's probably fuel pump check valve. My car had some trouble re-starting (had to crank it for ~10 seconds with the starter) after sitting on the slope with passanger side being below.
So, I guess, next step is replacing the check valve.

JamesE

I had what I thought was pinking at low revs when I just started the car, would disappear after a while, turned out to be the head gasket.

9x8

Yep, replaced the FP check valve and it fixed the problem.
No hesitation in those double-cluth downshifts anymore.

FRporscheman

9x8, I will order a new check valve. It's cheap and even if it's not my culprit, after seeing 236k miles worth of fuel, it's probably not doing too great.

Nice work!